Handle uppercase cbr state in perf output

[yinli-systems]

Fixes #324.

Summary

• allow uppercase state markers in cbr perf output before the second cbr: payload
• add an expect regression test using the perf line from "exception raised while parsing perf output" with "cbr: 36 freq: 3629 MHz (450%)" #324

Root cause

perf_cbr_event_re only allowed lowercase letters in the optional text between the event name and the frequency payload. On Ubuntu 24.04 / perf 6.8, perf can emit uppercase state text such as D, so parsing raised before extracting the frequency.

Validation

• git diff --check
• regex smoke with the same header/cbr regex shape over the existing cbr examples plus the "exception raised while parsing perf output" with "cbr: 36 freq: 3629 MHz (450%)" #324 D ... cbr: 36 freq: 3629 MHz (450%) line

I could not run the OCaml expect suite locally because this machine does not have ocaml, dune, or opam installed.