Feature - Improve the OnlineHelper

[iskandergaba]

• Improve the OnlineHelper accuracy by recalculating the rfft using STFT every buffer_size samples to prevent error accumulation.
• Enhance the OnlineHelper performance by vectorizing the rfft update operations to handle batch updates more efficiently.
• Refactor the internal parts for a cleaner API representation.

[codecov]

Codecov Report

Attention: Patch coverage is 99.08676% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pyriodicity/_internal/online_helper.py	96.42%	2 Missing ⚠️

Files with missing lines	Coverage Δ
pyriodicity/_internal/utils.py	96.66% <ø> (ø)
pyriodicity/online/online_acf.py	100.00% <100.00%> (ø)
pyriodicity/online/online_fft.py	100.00% <100.00%> (ø)
pyriodicity/static/acf.py	100.00% <100.00%> (ø)
pyriodicity/static/autoperiod.py	97.05% <100.00%> (ø)
pyriodicity/static/cfd_autoperiod.py	100.00% <100.00%> (ø)
pyriodicity/static/fft.py	100.00% <100.00%> (ø)
pyriodicity/static/robustperiod.py	99.23% <100.00%> (ø)
tests/conftest.py	100.00% <100.00%> (ø)
tests/online/test_online_acf.py	100.00% <100.00%> (ø)
... and 3 more

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