Preserve PySerial URLs when opening ASRL resources on Windows

[CAOShurong]

Follow-up to the serial URL support introduced in #386 and discussed in #385.

On Windows, SerialSession.after_parsing prefixes every board with COM before
calling serial_for_url. That is necessary for numeric VISA boards, but turns
loop:// and socket://... into unknown comloop / comsocket protocols.
The documented URL resources therefore cannot open on Windows, including the
socket handler used for TCP-to-serial converters.

Only add the prefix when the board has no ://, matching PySerial's own URL
dispatch. Numeric Windows boards still map to COM ports, POSIX device names are
unchanged, and custom URL handlers are not restricted to a built-in whitelist.
Discovery, serial attributes, I/O, error mapping and session lifetime are unchanged.

Regression coverage checks exact forwarding of six URL forms under both values
of the platform flag, native COM/POSIX mapping, and a real PySerial loopback through
ResourceManager.open_resource. The existing loopback test is unchanged.

Validation on Windows, Python 3.13.1, PyVISA 1.16.2 and PySerial 3.5:

• Exact-main, noneditable installed API: direct PySerial loop/socket controls
  succeed, while six VISA URL cases fail before the fix. The new regression
  suite is 8 failed / 13 passed before the repair.
• python -m pytest pyvisa_py/testsuite/test_serial.py -q: 21 passed, repeated.
  Serial/session/high-level subset: 24 passed.
• Complete suite: baseline 334 passed / 131 skipped / 1 failed; committed source
  and independently installed wheel each 353 passed / 131 skipped. All 465 other
  existing outcomes are unchanged; the existing serial failure is fixed and
  18 added cases pass. All 484 source/installed outcomes match.
• Full Ruff, configured python -m pre_commit run --all-files, strict Sphinx
  HTML build, sdist-to-wheel build, noneditable install and pip check: passed.
  A separate full mypy run in the fuller measurement environment reports the
  same two pre-existing tcpip.py:2102 errors on base and head; this is not an
  unconditional full-type-check-green claim.
• Eight installed API checks, repeated, and four installed pyvisa-info /
  pyvisa-shell --backend py paths pass: loopback and synthetic local socket
  query/binary I/O, read timeout/recovery, close, unknown handler, refused
  connection and malformed URL. Git, sdist, wheel and installed Python bytes
  were compared. Initial harness assumptions were corrected against direct
  PySerial controls; the original failed runs were retained.

Physical COM/RS232 instruments, an RFC2217 server, vendor/Keysight instrumentation,
other local OS/Python versions and production acquisition were not tested. The
socket peer is a synthetic echo endpoint, not independent hardware validation;
the platform-flag cases do not establish native Linux/macOS execution.

Disclosure: Codex generated/edited the code, tests, validation harnesses and this
PR text. No personal human review is claimed.

• Executed configured pre-commit hooks without errors
• Added automated regression coverage
• Added an entry to CHANGES
• Issue-closing keyword: not applicable; [COM] Communication issue loop #385 was already closed by replace the call to serial.Serial with serial.serial_for_url #386.
• Documented Windows COM/POSIX board formats and URL resources in
  docs/source/compliance.rst; corrected the loop/socket examples in index.rst.
  The earlier URL-handler note was in docs/source/index.rst, but the compliance
  notes were missing this information. This restores existing URL routing; no
  new interface or protocol-compliance behavior is introduced.

[hb020]

• Documentation/compliance changes: not applicable; this restores the existing
  documented URL routing, without a new interface or protocol-compliance change.

Well, it would be nice to document the different types of serial board formats accepted in /docs/source/compliance.rst, in the notes just under the top section Supported VISA resources. That is missing now. Same goes for USB boards, but someone else is working on that.

this restores the existing documented URL routing

Where is this? Maybe I'm missing something.

[CAOShurong]

Added the ASRL board formats and URL-handler examples to the Supported VISA resources notes in compliance.rst, including explicit-open/discovery limitations.

The earlier "documented" reference was the URL-handler note in index.rst, not the compliance notes; that omission is now corrected. Also fixed ASLRloop to ASRLloop and supplied the socket host/port in the examples.

Strict Sphinx HTML build passes; serial tests pass twice (21 each), and the full suite is 353 passed / 131 skipped. USB notes are untouched.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.23%. Comparing base (eee01cc) to head (1bffd43).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #664      +/-   ##
==========================================
+ Coverage   54.74%   57.23%   +2.48%     
==========================================
  Files          39       39              
  Lines        6518     6542      +24     
  Branches      649      650       +1     
==========================================
+ Hits         3568     3744     +176     
+ Misses       2854     2688     -166     
- Partials       96      110      +14     

Flag	Coverage Δ
unittests	57.23% <100.00%> (+2.48%)	⬆️

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[MatthieuDartiailh]

@CAOShurong can you address the merge conflict