_preserve_unicode_in_replacement now takes the matched region directly
instead of (content, [span]) wrapped per call, and the normalized
old_string plus its old->new opcodes - identical for every match - are
computed once per replace_all rather than once per match.
The replace_all Unicode regression test moves to a pure
fuzzy_find_and_replace test in tests/tools/test_fuzzy_match.py, replacing
the registry-driven test_patch_unicode_replace_all.py.
992f7807bf