Skip the value of an overridden DEBUGPY_EXTRA_ARGV switch

[Alexandre Kohler (kwy404)]

When a switch in DEBUGPY_EXTRA_ARGV was already given on the command line, parse_args_helper() skips the switch so that the command line takes precedence (as intended in #1624), but it does not skip the switch's value. That value is then parsed as the next argument, and a bare value is taken as a positional file target.

Repro:

DEBUGPY_EXTRA_ARGV="--connect 5678" python -m debugpy --connect 8888 -m spam

--connect 5678 is skipped, but 5678 is then parsed as a file target, so the options end up with target_kind == "file" and target == "5678" instead of the spam module. With a positional file target on the command line the stray value happens to be skipped as a duplicate target, which is why test_override_environment_switch passes today.

The fix consumes the value too when skipping a switch that takes one. Switches without a value and the positional target are unchanged.

Testing:

• Added test_override_environment_switch_with_module_target to tests/debugpy/server/test_cli.py. It fails on main (assert 'file' == 'module') and passes with the fix.
• tests/debugpy/server/test_cli.py: 95 passed on Windows, Python 3.12.
• flake8 and pyright report no new issues on the changed files.

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[Rich Chiodo (rchiodo)]

🔒 Automated review in progress — Rich Chiodo (@rchiodo) is auto-reviewing this PR.

[Rich Chiodo (rchiodo)]

Result: ⚠️ partially-verified

Verification details

Verification: The relevant tests could not be fully run in the isolated environment; this review is not fully verified.

Summary: The new module-target regression test passed. The complete CLI test file then passed with **95 tests** using the source tree via `PYTHONPATH=src`. The initial invocation could not collect because debugpy was not installed, and offline editable installation was blocked by a missing `wheel` package. Relevant behavioral coverage passed, but the unavailable standard installation path makes this partially verified.

Test runs: 2 passed, 1 not run

• ⚠️ Not run | CLI server tests (initial invocation) | python -Xfrozen_modules=off -m pytest -n0 -q tests/debugpy/server/test_cli.py
• ✅ Passed | PR module-target override regression test | PYTHONPATH=src .venv/bin/python -Xfrozen_modules=off -m pytest -n0 -q tests/debugpy/server/test_cli.py::test_override_environment_switch_with_module_target
• ✅ Passed | CLI server test file | PYTHONPATH=src .venv/bin/python -Xfrozen_modules=off -m pytest -n0 -q tests/debugpy/server/test_cli.py

⚠️ CLI server tests (initial invocation) diagnostic output

ImportError while loading conftest '/workspace/tests/conftest.py'.
tests/__init__.py:54: in <module>
    from debugpy.common import json, log
E   ModuleNotFoundError: No module named 'debugpy'

[Rich Chiodo (rchiodo)]

Approved via Review Center.

[Rich Chiodo (rchiodo)]

/azp run

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