fix: preserve DWARF markers at duplicate PCs

[swananan]

Summary

• inspect every DWARF line row at a PC when selecting prologue_end or the first statement address
• bound prologue and statement scans to the selected function range
• add a real GCC DWARF 5 -O3 -gcolumn-info regression and keep cached fixture build flags synchronized

Testing

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test -p ghostscope-dwarf index::line_mapping::tests -- --nocapture (18 passed)
• targeted partitioned-range and duplicate-PC e2e tests passed through the runner service
• full host-to-host e2e reached the existing rust_script_execution baseline failures (33 passed, 16 failed in that test binary); a representative failure was reproduced on unchanged main

Container-topology e2e was not run because this change does not affect container or PID-namespace behavior.