fix: parse LSP messages by byte length to fix multi-byte UTF-8 (CI + real-Zed verified)

[liuyanghejerry]

Problem

CI (Test LSP Server job) was failing: two tests in lib/data-parser.test.js under UTF-8 byte length handling — the parse callback was never invoked.

Root cause: LSP Content-Length is defined in bytes, but data-parser.js had been reverted to parse by character (stdinBuffer = '', substring). Any message containing multi-byte UTF-8 (e.g. textDocument/didOpen for an .ets file with Chinese content) is mis-sliced — the parser grabs too many characters, pulls the next message's header into the JSON, and JSON.parse throws. The document is silently dropped, so the language server never receives it → dead LSP for those files. The tests asserted the correct byte-based behavior, so they (correctly) failed.

This has been reverted the wrong way several times (c6cee0c → 1083e2d → a88ed44, plus 3b04512/052b8be). Each revert "worked" only because LSP startup traffic is ASCII.

Fix

lib/data-parser.js — restore Buffer-based parsing (Content-Length counted in bytes) with all three pieces the earlier reverts never had together:

1. Buffer buffer (Buffer.alloc(0), Buffer.concat, subarray, .toString('utf8'));
2. keep process.stdin.setEncoding('utf8') in index.js (its StringDecoder reassembles multi-byte chars split across TCP chunks);
3. a string→Buffer guard in parse() (Buffer.isBuffer(data) ? data : Buffer.from(data, 'utf8')) — because setEncoding yields strings and Buffer.concat([buf, string]) throws.

index.js — harden the initialize handler to forward the request as-is instead of crashing with Cannot read properties of undefined (reading 'tsdk') when initializationOptions isn't configured.

Verification

• Unit + integration + formatting: all 63 tests pass.
• Real Zed editor driving the real @arkts/language-server, opening a Chinese-heavy .ets file:
  • char-based → the 4698-char didOpen is dropped; wrapper logs Error parsing message: Unexpected non-whitespace character after JSON.
  • byte-based (this PR) → didOpen forwarded intact, 0 parse errors, no crash.

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