feat: add IEC 61260-1 nominal frequency labels (#46)
Add nominal frequency label support per IEC 61260-1:2014.
- New nominal parameter in octavefilter() and OctaveFilterBank.filter()
- getansifrequencies() returns 4-tuple with labels (breaking change)
- Bump version to 1.2.0
- Address review findings: np.isclose matching, lru_cache, sonar exclusions
Closes #44
Co-authored-by: ninoblumer <40544174+ninoblumer@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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