fix: collapse nested if into match guard to resolve clippy::collapsible_match

[Copilot]

CI was failing due to a clippy::collapsible_match error (enforced via -D clippy::all) in src/bam/ext.rs.

Change

Collapsed the nested if inside the Cigar::HardClip match arm into a match guard:

// Before
Cigar::HardClip(len) => {
    if include_hard_clip {
        result += len;
    }
}

// After
Cigar::HardClip(len) if include_hard_clip => {
    result += len;
}