Release 0.2.0

[andremsouza]

Ships the corrected Mexican hat from #2, plus three packaging fixes.

Changes

• Version 0.2.0. The repository said 0.1.2 while PyPI was already at 0.1.3.
• Restored the cli extra. It shipped in 0.1.3 on PyPI but was never committed. Releasing from
  the repository as-is would have silently broken pip install python-som[cli] for existing users.
• requires-python corrected to >=3.10. The declared >=3.9 was never accurate: the module
  uses PEP 604 unions (int | None) in runtime-evaluated annotations with no
  from __future__ import annotations, so importing it on 3.9 raises TypeError. Installers now
  decline the package there rather than install something unimportable. 3.9 reached EOL in
  October 2025.
• Added CHANGELOG.md, documenting the behavior changes with their citations, and recording
  that 0.1.3 was published from an uncommitted working tree and has no corresponding commit.

Verification

twine check dist/*                          both artifacts PASSED
wheel -> clean venv -> import               version 0.2.0
h(c)                                        1.0
mexican hat diagonal at 2 sigma             -0.054947  (negative, as required)
mexican hat minimum                         -0.135335  (= -exp(-2))
batch + mexicanhat                          ValueError raised
pip install 'python_som[cli]'               tqdm 4.70.0 pulled in

Also removed a stray untracked SOM_atualizado.py from the working tree, which hatchling had been
sweeping into the sdist. It was an abandoned experimental variant and would have been published to
PyPI otherwise. Preserved outside the repository rather than deleted.

Next up is the packaging modernization to 0.3.0.