Address three critical safety issues found during codebase audit:
- glob.rs: Explicitly drop ThreadsafeFunction after glob operation
completes to release the N-API reference immediately instead of
relying on implicit drop ordering.
- ttsr.rs: Add handle bounds validation in ttsrCheckBuffer, recover
from mutex poisoning via unwrap_or_else instead of returning errors,
cap live handles at 10,000 to prevent unbounded growth, and add
ttsrClearAll for bulk cleanup.
- image.rs: Replace unchecked (w * h * N) as usize casts with
checked_mul arithmetic that returns a descriptive error instead of
panicking on overflow.
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