Reduce memory usage in changelog generation and release copying

[JakeShirley]

Summary

Reduces peak memory usage during changelog generation by eliminating redundant object cloning.

Changes

1. Share changelog by reference instead of N deep copies (changelog.ts)

Previously, each module in a group received its own JSON.parse(serializedChangelog). For large modules like @minecraft/server with 36 version groups x N modules, this created hundreds of MB of identical objects. Now we parse once and assign the same reference to all modules in the group. This is safe because nothing mutates the originals before MinecraftRelease.copy() deep-clones them downstream.

2. Remove unnecessary deepCopyJson of layout keys (changelog.ts)

Layout keys (e.g. name) are always primitives (strings/numbers) that don't need deep copying.

3. Batch release.copy() serialization (MinecraftRelease.ts)

Refactored copy() to serialize each module array as a whole (JSON.parse(JSON.stringify(arr))) instead of per-element, using a generic deepCopyArray<T> helper. Reduces JSON.stringify/parse call overhead.

Benchmark (5 Minecraft releases, 285 MB metadata input)

Metric	Before	After	Change
Peak heap (changelog gen)	723 MB	352 MB	-51%
Heap after gen (GC'd)	602 MB	242 MB	-60%
Overall peak heap	1,189 MB	828 MB	-30%

Output is byte-identical. All 57 snapshot tests pass.