Expose `GetPowderPatternObsSigma` and `SetPowderPatternObsSigma` (#84) #7

Job	Run time
matrix-coverage / get-python-versions / get-python-versions	4s
matrix-coverage / coverage (windows-latest, 3.12)	10m 37s
matrix-coverage / coverage (windows-latest, 3.14)	11m 59s
matrix-coverage / coverage (macos-latest, 3.14)	4m 47s
matrix-coverage / coverage (ubuntu-latest, 3.14)	5m 6s
matrix-coverage / coverage (ubuntu-latest, 3.12)	5m 8s
matrix-coverage / coverage (macos-latest, 3.13)	5m 11s
matrix-coverage / coverage (macos-15-intel, 3.13)	7m 36s
matrix-coverage / coverage (windows-latest, 3.13)	9m 24s
matrix-coverage / coverage (macos-latest, 3.12)	4m 15s
matrix-coverage / coverage (ubuntu-latest, 3.13)	5m 13s
matrix-coverage / coverage (macos-15-intel, 3.14)	7m 34s
matrix-coverage / coverage (macos-15-intel, 3.12)	12m 7s
	1h 29m 1s

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