Parse uppercase flags in perf CBR events

[jeet-dekivadia]

Summary

• accept uppercase letters in the ignored annotation prefix of perf CBR events
• add a regression using the Ubuntu 24.04 perf script line from the issue

Why

Newer perf output can include an uppercase D marker before the CBR payload. The parser only accepted lowercase annotation text there, so Re.exec raised Not_found before the frequency event could be decoded.

Validation

• git diff --check
• exercised the widened CBR pattern against the reported line and confirmed it extracts 3629 MHz
• added expect coverage for the reported parser path

Fixes #324

[jeet-dekivadia]

I rechecked this today while it is waiting for review. The parser change is limited to accepting uppercase annotation flags in perf CBR event lines, matching the shape emitted by newer perf versions such as Ubuntu 24.04's D flag output.

The extraction path for the CBR value is otherwise unchanged; the regression keeps the reported uppercase-flag line decoding to the expected MHz value. DCO is green, and the PR has no red checks.