chore(8.0): modernize toolchain + position Bun as a runtime

Consumer-invisible modernization pass — no public API or runtime-behavior
change; dist for the override-only files is byte-identical.

Toolchain:
- CI: GitHub Actions matrix — Node 22/24 (test:unit) + Bun latest (test:bun).
- engines: node ">=22" (was "22.x"), bun ">=1.1.0".
- tsconfig: isolatedModules + noImplicitOverride; add the 33 `override`
  modifiers the flag requires across storage/integrations/vfs/transaction.
- deps: @types/node ^22; add prettier; drop dead standard-version,
  @rollup/plugin-* and the redundant embedded eslintConfig (flat
  eslint.config.js is the active config — verified identical lint output).

paramValidation: replace the top-level `await import('node:os'/'node:fs')`
with static ESM imports. The top-level-await form poisoned the module graph;
static imports also drop the browser/edge fallback branches no supported
runtime reaches (8.0 is Node/Bun/Deno-only).

Bun positioning: recommend Bun as a runtime (`bun add` / `bun run`), which is
green (test:bun 8/8). Drop single-binary `bun build --compile` as a target —
native addons cannot embed into it, and Bun 1.3.10 has a `--compile` codegen
regression around top-level await. Rename the Bun test to bun-runtime-test.ts
and correct docs that overclaimed single-binary support.

Gates: typecheck 0, build 0, test:unit 1743/1743, test:bun 8/8.

src/vfs/streams/VFSReadStream.ts

@@ -25,7 +25,7 @@ export class VFSReadStream extends Readable {
     this.position = options.start || 0
   }
 
-  async _read(size: number): Promise<void> {
+  override async _read(size: number): Promise<void> {
     try {
       // Lazy load entity
       if (!this.entity) {
@@ -58,7 +58,7 @@ export class VFSReadStream extends Readable {
     }
   }
 
-  _destroy(error: Error | null, callback: (error?: Error | null) => void): void {
+  override _destroy(error: Error | null, callback: (error?: Error | null) => void): void {
     // Clean up resources
     this.entity = null
     this.data = null

src/vfs/streams/VFSWriteStream.ts

@@ -28,7 +28,7 @@ export class VFSWriteStream extends Writable {
     }
   }
 
-  async _write(
+  override async _write(
     chunk: any,
     encoding: BufferEncoding,
     callback: (error?: Error | null) => void
@@ -52,7 +52,7 @@ export class VFSWriteStream extends Writable {
     }
   }
 
-  async _final(callback: (error?: Error | null) => void): Promise<void> {
+  override async _final(callback: (error?: Error | null) => void): Promise<void> {
     try {
       await this._flush()
       callback()
@@ -78,7 +78,7 @@ export class VFSWriteStream extends Writable {
     this.chunks = []
   }
 
-  _destroy(error: Error | null, callback: (error?: Error | null) => void): void {
+  override _destroy(error: Error | null, callback: (error?: Error | null) => void): void {
     // Clean up resources
     this.chunks = []
     this._closed = true