Optimize Turnkey classifier case-insensitive search

[RAprogramm]

Summary

• precompute lowercase classifier needles once, reuse stack buffers for short strings, and update the docs/tests to reflect the minimal-allocation behaviour
• add regression coverage for long Turnkey needles and document the fallback allocation strategy
• bump the crate to v0.10.7 and refresh README/CHANGELOG version references

Testing

• cargo +1.90.0 build --all-targets
• cargo +1.90.0 test --all
• cargo +1.90.0 clippy -- -D warnings
• cargo +1.90.0 doc --no-deps
• cargo deny check
• cargo audit

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https://chatgpt.com/codex/tasks/task_e_68cf377f175c832bbd5c68a0aedc6c85