**chore: introduce unified Rollup configuration for browser and Node.js builds**

### Changes:
- Added `rollup.config.js` with custom build logic for unified and browser builds:
  - Included TypeScript support with separate configurations (`tsconfig.unified.json` and `tsconfig.browser.json`).
  - Consolidated environment detection logic with `globalThis.__ENV__` for browser, Node.js, and serverless environments.
  - Provided global Buffer polyfill for browser environments.
  - Enabled `inlineDynamicImports` for module compatibility.
- Introduced custom Rollup plugins:
  - Shims for Node.js built-in modules to ensure compatibility in browsers.
  - Fixes for `this` references in TensorFlow.js layers causing errors in browser environments.
- Enabled environment-specific replacements for `process.env.NODE_ENV` during builds.
- Configured outputs for both non-minified and minified builds (`.js` and `.min.js` files).
- Excluded specific dependencies from the bundle to optimize build size.

### Purpose:
Added a versatile Rollup configuration to streamline the build process for both browser and Node.js environments. This setup enhances cross-environment compatibility, reduces redundancy, and ensures better maintainability with unified build logic.

rollup.config.js

@@ -0,0 +1,176 @@
+import typescript from '@rollup/plugin-typescript'
+import resolve from '@rollup/plugin-node-resolve'
+import commonjs from '@rollup/plugin-commonjs'
+import json from '@rollup/plugin-json'
+import { terser } from 'rollup-plugin-terser'
+import replace from '@rollup/plugin-replace'
+
+// Custom plugin to provide empty shims for Node.js built-in modules in browser environments
+const nodeModuleShims = () => {
+  return {
+    name: 'node-module-shims',
+    resolveId(source) {
+      // List of Node.js built-in modules to shim
+      const nodeBuiltins = [
+        'fs',
+        'path',
+        'util',
+        'crypto',
+        'os',
+        'stream',
+        'http',
+        'http2',
+        'https',
+        'zlib',
+        'child_process'
+      ]
+
+      if (nodeBuiltins.includes(source)) {
+        // Return a virtual module ID for the shim
+        return `\0${source}-shim`
+      }
+      return null
+    },
+    load(id) {
+      // If this is one of our shims, return an empty module
+      if (id.startsWith('\0') && id.endsWith('-shim')) {
+        console.log(
+          `Providing empty shim for Node.js module: ${id.slice(1, -5)}`
+        )
+        return 'export default {}; export const promises = {};'
+      }
+      return null
+    }
+  }
+}
+
+// Custom plugin to fix 'this' references in specific files
+const fixThisReferences = () => {
+  return {
+    name: 'fix-this-references',
+    transform(code, id) {
+      // Only transform the specific files that have issues with 'this'
+      if (
+        id.includes(
+          '@tensorflow/tfjs-layers/dist/layers/convolutional_recurrent.js'
+        )
+      ) {
+        // Replace 'this' with 'globalThis' in the problematic code
+        return {
+          code: code.replace(/\bthis\b/g, 'globalThis'),
+          map: { mappings: '' } // Provide an empty sourcemap to avoid warnings
+        }
+      }
+      return null // Return null to let Rollup handle other files normally
+    }
+  }
+}
+
+// Get build type from environment variable or default to 'unified'
+const buildType = process.env.BUILD_TYPE || 'unified'
+
+// Configuration based on build type
+const config = {
+  unified: {
+    input: 'src/unified.ts',
+    outputPrefix: 'unified',
+    tsconfig: './tsconfig.unified.json',
+    declaration: true,
+    declarationMap: true,
+    intro: `
+// Environment detection
+const isBrowser = typeof window !== 'undefined';
+const isNode = typeof process !== 'undefined' && process.versions && process.versions.node;
+const isServerless = !isBrowser && !isNode;
+
+// Global Buffer polyfill for browser environments
+if (isBrowser) {
+  try {
+    // Import Buffer from the buffer package
+    import('buffer').then(({ Buffer }) => {
+      globalThis.Buffer = Buffer;
+    }).catch(err => {
+      console.warn('Failed to load Buffer polyfill:', err);
+    });
+  } catch (e) {
+    console.warn('Failed to import buffer package:', e);
+  }
+}
+
+// Global variable to store environment
+globalThis.__ENV__ = {
+  isBrowser,
+  isNode,
+  isServerless
+};
+    `
+  },
+  browser: {
+    input: 'examples/browser_compatible_exports.ts',
+    outputPrefix: 'brainy',
+    tsconfig: './tsconfig.browser.json',
+    declaration: false,
+    declarationMap: false,
+    intro: 'var global = typeof window !== "undefined" ? window : this;'
+  }
+}
+
+// Get configuration for the current build type
+const buildConfig = config[buildType]
+
+// Create the rollup configuration
+export default {
+  input: buildConfig.input,
+  output: [
+    {
+      dir: 'dist',
+      entryFileNames: `${buildConfig.outputPrefix}.js`,
+      format: 'es',
+      sourcemap: true,
+      inlineDynamicImports: true,
+      intro: buildConfig.intro
+    },
+    {
+      dir: 'dist',
+      entryFileNames: `${buildConfig.outputPrefix}.min.js`,
+      format: 'es',
+      sourcemap: true,
+      inlineDynamicImports: true,
+      intro: buildConfig.intro,
+      plugins: [terser()]
+    }
+  ],
+  plugins: [
+    // Add environment replacement for unified build
+    ...(buildType === 'unified' ? [
+      replace({
+        preventAssignment: true,
+        'process.env.NODE_ENV': JSON.stringify('production')
+      })
+    ] : []),
+    // Add our custom plugins
+    fixThisReferences(),
+    nodeModuleShims(),
+    resolve({
+      browser: true,
+      preferBuiltins: false
+    }),
+    commonjs({
+      transformMixedEsModules: true
+    }),
+    json(),
+    typescript({
+      tsconfig: buildConfig.tsconfig,
+      declaration: buildConfig.declaration,
+      declarationMap: buildConfig.declarationMap
+    })
+  ],
+  external: [
+    // Add any dependencies you want to exclude from the bundle
+    '@aws-sdk/client-s3',
+    '@smithy/util-stream',
+    '@smithy/node-http-handler',
+    '@aws-crypto/crc32c',
+    'node:stream/web'
+  ]
+}