[Feature] Support Android as a posix platform

[NTFSvolume]

On Python 3.13+, sys.platform reports android as a valid platform instead of just linux

Installing a package on Termux that uses readchar throws the following exception on startup:

File "/data/data/com.termux/files/home/.local/share/uv/tools/cyberdrop-dl-patched/lib/python3.13/site-packages/inquirer/events.py", line 1, in <module>
    import readchar
  File "/data/data/com.termux/files/home/.local/share/uv/tools/cyberdrop-dl-patched/lib/python3.13/site-packages/readchar/__init__.py", line 21, in <module>
    raise NotImplementedError(f"The platform {platform} is not supported yet")
NotImplementedError: The platform android is not supported yet

Adding android to the check here was enough to fix it for me:

python-readchar/readchar/__init__.py

Line 14 in 753cb42

if platform.startswith(("linux", "darwin", "freebsd", "openbsd")):

Everything is working as expected AFAIK. I will try to run the test suite and report back

[NTFSvolume]

After some similar modifications to conftest.py, everything passes:

======================================= warnings summary =======================================
../../../../data/data/com.termux/files/usr/lib/python3.13/site-packages/coverage/core.py:108
  /data/data/com.termux/files/usr/lib/python3.13/site-packages/coverage/core.py:108: CoverageWarning: Couldn't import C tracer: No module named 'coverage.tracer' (no-ctracer); see https://coverage.readthedocs.io/en/7.13.5/messages.html#warning-no-ctracer
    warn(f"Couldn't import C tracer: {IMPORT_ERROR}", slug="no-ctracer", once=True)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================================== tests coverage ========================================
______________________ coverage: platform android, python 3.13.12-final-0 ______________________

Name                      Stmts   Miss  Cover
---------------------------------------------
readchar/__init__.py         13      4    69%
readchar/_base_key.py        31      0   100%
readchar/_config.py           6      1    83%
readchar/_posix_key.py       30      0   100%
readchar/_posix_read.py      30      1    97%
readchar/_win_key.py         28     28     0%
readchar/_win_read.py        14     14     0%
readchar/key.py               5      5     0%
---------------------------------------------
TOTAL                       157     53    66%
================================ 273 passed, 1 warning in 8.74s ================================
/sdcard/python-readchar $

[NTFSvolume]

• Sorry, this is already addressed on this PR: Add android as supported platform #130