fix(chimeric): well-formed single-end WithinBAM records with STAR's hard-clip rules

[BenjaminDEMAILLE]

Closes #279.

Root cause: build_within_bam_records used each segment's CIGAR as is and gave the representative the full read SEQ. SE soft-clip re-mapping (Tier 1b) and residual re-seeding (Tier 3) re-align a sub-sequence and only shifted exon coordinates, so the CIGAR was never padded (e.g. 40M with a 100 bp SEQ) and reverse-strand pieces got forward-read coordinates. Related bugs: Tiers 1b/2/3 ordered segments without accounting for strand, Tier 1b took the clip from the wrong end for a reverse primary, and Tier 3 then re-found a covered segment (duplicate chimera).

Fix (checked against STAR ChimericAlign_chimericBAMoutput.cpp, ReadAlign_alignBAM.cpp):

• CIGARs padded with soft clips to full read length (full_length_cigar); lift_clip_transcript maps sub-sequence transcripts into full-read orientation.
• SE: segments ordered by read position (STAR trChim), representative = strictly higher score else second (chimRepresent), supplementary hard-clipped on its junction side (itr%2==Str ? -12 : -11), SEQ trimmed accordingly. --chimOutType WithinBAM SoftClip keeps soft clips (new chim_out_bam_hard_clip()).
• SA tags use the other record's final CIGAR.
• PE: behaviour unchanged apart from padded CIGARs.
• May change donor/acceptor order in Chimeric.out.junction for affected SE reads.

Tests: integration test test_se_chim_within_bam_records_well_formed (HardClip and SoftClip; fails on main with the reported error), plus 4 unit tests. fmt, clippy 0 warnings, all suites green.

Remaining STAR differences (not in this PR):

1. STAR skips the read's normal alignment when a chimera goes into the BAM; rustar still writes it (affects Log.final.out too).
2. rustar can emit more than one chimera per read (Tiers 2/3 are rustar-only).
3. PE WithinBAM: no mate fields/paired flags, no hard clips, and inter-mate chimeras (STAR chimType 2) written with one supplementary record.
4. QUAL empty on chimeric records.

Tracking: #277

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