Speed up XML generation and update Rust to 1.93.1

[bokuweb]

Summary

• stream encoded start tags directly instead of retaining a second pending buffer
• box EventWriter internal state so XMLBuilder ownership transfers move one pointer
• reduce the start-element inline buffer from 128 to 64 bytes
• update the repository Rust toolchain from 1.88 to 1.93.1

Performance

Criterion benchmarks on Apple Silicon:

Benchmark	Before	After	Improvement
write_docx_build	1.979 ms	1.052 ms	46.8%
write_docx_build_pack	3.080 ms	1.950 ms	36.7%
write_docx_large_build_pack	25.25 ms	20.11 ms	20.3% before the final boxing optimization
write_docx_many_static_tocs	10.30 ms	7.50 ms	27.3% before the final boxing optimization

After boxing the writer state, XMLBuilder::add_child dropped from about 9.7% to about 1.0% of sampled top-of-stack frames.

Validation

• 327 library unit tests passed
• 62 integration tests passed
• cargo clippy -p docx-rs --lib -- -D warnings
• cargo fmt --all -- --check

The tests and focused final benchmarks were run with Rust 1.93.1.

[github-actions]

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change	0
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