fix: preserve ANSI escapes while stripping manpage overstrike

[sjh9714]

Summary

• Preserve ANSI escape sequences that appear between an overstruck character and the following backspace.
• Prevent manpage overstrike stripping from truncating SGR resets like \x1b[22m into broken sequences such as \x1b[22v.
• Add unit and integration regression coverage for the manpage path.

Testing

• PATH="$HOME/.cargo/bin:$PATH" cargo test test_strip_overstrike_preserves_ansi_before_backspace
• PATH="$HOME/.cargo/bin:$PATH" cargo test --test integration_tests strip_overstrike_for_manpage_syntax_keeps_ansi_escapes_intact
• PATH="$HOME/.cargo/bin:$PATH" cargo test --locked strip_overstrike
• PATH="$HOME/.cargo/bin:$PATH" cargo fmt --check
• PATH="$HOME/.cargo/bin:$PATH" cargo test --locked

Refs #3724