Fix TIMESTAMP(10..12) fetch performance issue(#1079) and drop Python 3.9/3.10 wheel builds

[Earammak]

Summary

Fix for #1079.
Fetching TIMESTAMP columns with fractional precision greater than 9 (TIMESTAMP(10..12)) raised a CLI0182W (SQLSTATE 01S07) truncation warning for every fetched row. The resulting diagnostic handling introduced significant fetch overhead.

This PR updates timestamp binding to use extended timestamp structures for high-precision timestamps and removes Python 3.9 and 3.10 support.

Changes

• ibm_db.c: bind TIMESTAMP columns with scale > 9 using SQL_C_TIMESTAMP_EXT
  (TIMESTAMP_STRUCT_EXT) instead of TIMESTAMP_STRUCT. This covers
  single-row fetch (SQLBindCol), rowset fetch, and the cleanup paths.

• Python values are unchanged: datetime.datetime with microsecond precision.

• ibm_db.c (ibm_db_fetch_callproc): the debug log messages for array and
  scalar TIMESTAMP output parameters now show whether the type is TIMESTAMP or
  TIMESTAMP WITH TIME ZONE. The two types share a case branch and were both
  logged as TIMESTAMP.

• .github/workflows/bld_wheels_and_upload.yml: skip cp39/cp310/pp39/pp310 in
  all cibuildwheel jobs (Windows, Linux, macOS), so 3.9 and 3.10 wheels are no
  longer built.

• setup.py: remove the 3.9/3.10 classifiers.

• README: Update supported Python version range and add timestamp precision notes.

• Tests: add test_6794 and async test_37 for timestamp precision fetch.