Define the public API in otava/__init__.py

[MrlixiangWE]

Expose nine names from otava, including Series, AnalysisOptions and
compute_change_points, and document their use in docs/API.md. Existing
submodule imports remain available.

The package root now loads SciPy, so importing a lightweight module such as
otava.csv_options also loads those dependencies.
Median import overhead in milliseconds, measured over 21 runs per checkout,
alternating base and branch, on a 4-core QEMU/KVM VM with Python 3.12.14.
Each sample subtracts a separate Python startup measurement, which can yield
negative estimates.

Import	d2d51c9	610066f
otava	-1	593
otava.csv_options	17	581
otava.util	168	818
otava.series	598	601
otava.main	842	866

The tests check the documented export names against __all__, check option
names and defaults against AnalysisOptions(), and run the documentation
examples. The wheel smoke test checks the installed package's exports and
calls compute_change_points without extras.

Verified on Ubuntu 22.04 / x86_64 with uv sync --locked --all-extras --dev:
248 tests passed on each of Python 3.10.21, 3.11.16, 3.12.14, 3.13.15 and
3.14.7; the same suite passed 241 tests on d2d51c9. This covers tests and
perf, excluding the Graphite, PostgreSQL and InfluxDB container e2e modules.
On Python 3.12.14, sphinx-build -W --keep-going passed on both checkouts.
A wheel built from this branch passed tests/core_install_smoke.py in an
installation without extras.

Closes #101

[henrikingo]

Thanks MirliangWE! I hope to review this soon.Defining an API for Otava use in a library is a valuable addition.

[MrlixiangWE]

Thanks, Henrik! I’ve also pushed a small follow-up to clarify the documentation around timestamp handling and the supported import surface.