inflate: skip the per-match bounds check in the fast loop

[jlucaso1]

The inflate fast loop already guarantees INFLATE_FAST_MIN_LEFT bytes of output headroom before it runs, yet copy_match still recomputes a capacity clamp and does a bounds check on every single match. That work is redundant inside the fast loop.

This adds a copy_match_unchecked variant used only there, and bumps the margin to also cover the chunked copy's overshoot (260 + 32), so the per-match check can be safely elided. zlib-ng/libdeflate do the same thing.

Measured ~8% fewer instructions on inflate (perf stat, on a mix of protobuf-like data and the silesia corpus). The window-copy path is untouched.

Correctness: the full test-libz-rs-sys C-compat suite passes, plus a fuzz roundtrip (200k random inputs across sizes/levels) with a canary past the output buffer to catch any overshoot.