fix(core): lazily allocate text buffer syntax styles

[kadary]

Summary

• Lazily allocate native SyntaxStyle handles only when styled text requires them, with explicit ownership and destruction guards.
• Encapsulate buffer mutations behind protected seams and expose typed TextRenderable file-loading APIs for the text-wrap example.
• Add regression coverage for lazy allocation, styled chunks, lifecycle cleanup, post-destroy protection, TextNode styling, and file-load layout updates.

Validation

• bun test src/renderables/TextBufferRenderable.test.ts from packages/core — 6 passing.
• Targeted core renderable tests — 186 passing, 1 skipped.
• React tests — 52 passing.
• Solid tests — 265 passing.
• bun run lint — 0 warnings/errors.
• bun run fmt:check — passing.
• tsc --noEmit confirmed no errors in changed files; unrelated pre-existing project errors remain outside this diff.

Notes

• The complete core JavaScript suite showed intermittent failures in unrelated runtime-plugin/audio-stream tests across repeated runs. The new regression test was not implicated.