Add versioned bytecode file support to qjsc and qjs

[zzjjob]

Supersedes #540, which was automatically closed when the source fork was recreated.

Summary

• add qjsc -b / qjsc --bytecode to write compiled scripts or modules directly to .qbc files
• add qjs --bytecode to load and execute those files, including module resolution, top-level await, and script arguments
• wrap the serialized QuickJS object in a fixed 64-byte header containing a magic value, CONFIG_VERSION, payload length, checksum, and reserved flags
• reject unsupported versions, malformed headers, size mismatches, unsupported flags, and corrupted payloads before deserialization
• run the existing test suite through both source and bytecode-file paths

Motivation

qjsc currently emits C source or native executables, but it does not provide a direct file artifact for applications that want to compile JavaScript once and execute it later with the same QuickJS build. Using the raw JS_WriteObject() payload directly also provides no framing for compatibility or integrity checks.

This change adds a small versioned container around the existing QuickJS bytecode representation. Files are intentionally bound to the exact QuickJS CONFIG_VERSION; bytecode from another version is rejected with a clear diagnostic.

Usage

qjsc --bytecode -o app.qbc app.js
qjs --bytecode app.qbc arg1 arg2

qjsc --bytecode -m -o module.qbc module.mjs
qjs --bytecode module.qbc

When -o is omitted, qjsc --bytecode writes out.qbc. Bytecode output accepts exactly one input file and is not combined with byte-swapping.

File format and trust model

The wrapper validates container structure, QuickJS version, payload length, and an FNV-1a checksum. The checksum detects accidental corruption; it is not a cryptographic signature or a sandbox boundary. As with other native bytecode formats, .qbc files should be loaded only from trusted sources.

Tests

• make test
• source and generated-QBC execution for the existing language, builtin, loop, bigint, module, worker, std, and read/write handler tests
• script arguments and ES module execution with top-level await
• clean rejection of bad magic, version mismatch, and checksum corruption

This PR contains only commit a2c571acad9a4079fc0e29aacc4da7bbef94d4ff on top of master.