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Add branch prediction hints to deflate strategy hot loops

The deflate strategies were inconsistent about branch-prediction hints
on their per-iteration lookahead checks. deflate_quick marked both the
window-refill path unlikely and the steady-state path likely;
deflate_slow marked only the steady-state path; deflate_fast and
deflate_medium marked neither, leaving the compiler to guess the inner
loop's hot/cold block placement.

Mark the window-refill and end-of-input paths unlikely and the
steady-state path likely across deflate_fast, deflate_slow,
deflate_medium, deflate_rle, and deflate_huff, following deflate_quick,
so the rarely-taken refill block stays off the hot fall-through path
and block placement is consistent across all strategies.

2248 of 2405 branches covered (93.47%)

Branch coverage included in aggregate %.

9299 of 10673 relevant lines covered (87.13%)

17427311.72 hits per line