Enforce distribution name normalization for wheel filenames

[di]

In pypa/packaging.python.org#1032 it was resolved that distribution names in wheel filenames should be lowercased per PEP 503, and the binary distribution format spec was updated, but we never began enforcing this.

Similar to #12245, we should warn on upload during a deprecation period before eventually blocking uploads.

Currently usage is very low:

warehouse=> SELECT DATE(time) AS day, COUNT(additional->>'filename') AS file_count
FROM file_events
WHERE additional->>'filename' ~ '[A-Z]'
  AND additional->>'filename' LIKE '%.whl'
  AND time >= (CURRENT_DATE - INTERVAL '30 days')
GROUP BY day
ORDER BY day DESC;
    day     | file_count
------------+------------
 2025-01-09 |        197
 2025-01-08 |        309
 2025-01-07 |        394
 2025-01-06 |        292
 2025-01-05 |        188
 2025-01-04 |        265
 2025-01-03 |        463
 2025-01-02 |        290
 2025-01-01 |        136
 2024-12-31 |        329
 2024-12-30 |        199
 2024-12-29 |        222
 2024-12-28 |        170
 2024-12-27 |        306
 2024-12-26 |        271
 2024-12-25 |        111
 2024-12-24 |        275
 2024-12-23 |        245
 2024-12-22 |        209
 2024-12-21 |        131
 2024-12-20 |        329
 2024-12-19 |        292
 2024-12-18 |        309
 2024-12-17 |        499
 2024-12-16 |        406
 2024-12-15 |        179
 2024-12-14 |        200
 2024-12-13 |        577
 2024-12-12 |        406
 2024-12-11 |        303
 2024-12-10 |        408
(31 rows)

Ref: parent issue #12316.