perf(bytes): write escaped hex digits directly

[mizchi]

Summary

Write escaped byte hex digits directly to the output logger instead of allocating a two-character String via Byte::to_hex() for every escaped byte. The private helper is shared by Show and ToJson.

Benchmark

Native release, 100,000 binary bytes:

Operation	Before	After
Bytes Show	1.65 ms	544.43 us
Bytes ToJson	1.46 ms	508.42 us

Validation

• moon test builtin --target all
• moon check
• moon info (no interface changes)

[Copilot]

Pull request overview

Improves Bytes/BytesView escaping performance by writing hex digits directly to a Logger instead of allocating a 2-character String per escaped byte, and validates behavior with a targeted regression test and a benchmark.

Changes:

• Added a private write_byte_hex(&Logger, Byte) helper in builtin/bytesview.mbt to emit two lowercase hex digits without allocating.
• Updated Show and ToJson implementations for BytesView to use the new helper for \xHH escapes.
• Added a new behavior test ensuring lowercase hex output, plus a new benchmark test file for Bytes Show and ToJson on binary data.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
builtin/bytesview.mbt	Introduces write_byte_hex and switches BytesView Show/ToJson escaping to direct hex digit writes.
builtin/bytes_test.mbt	Adds a regression test asserting exact lowercase \xhh escaping for both Show and ToJson.
builtin/bytes_output_bench_test.mbt	Adds benchmarks for Bytes Show/ToJson on 100k binary bytes to quantify the perf impact.

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