Fix loadscope handling of colons in parameters

[LouisDeconinck]

Fixes #1335.

LoadScopeScheduling._split_scope previously split on the last ::, so a parametrized value containing :: could be mistaken for the test scope. Parse the module boundary first and only consider :: separators before parametrization, preserving class-level grouping.

Added regression coverage for colon-containing parameters and parameterized class methods.

Checks:

• Reasonable regression tests added
• Towncrier changelog fragment added
• pytest -q testing (224 passed, 6 skipped, 10 xfailed)
• ruff check and ruff format --check
• git diff --check

[LouisDeconinck]

Pushed a fix for the py311-pytestmain CI failures.

The failing TestGroupScope tests were unrelated to the loadscope change: pytest main (pytest-dev/pytest#14758, upcoming 9.2) replaced the Node._nodeid string with a structured NodeId object in Node._id, so item._nodeid = ... in remote.py silently wrote a dead attribute and the @group suffix never reached the scheduler — every test became its own scope.

The commit detects Node._id and overrides the NodeId's cached string form instead, so item.nodeid (and reports, which share the object) still carry the @group suffix; released pytest keeps the existing _nodeid path. Full testing/ suite passes locally against both pytest main and pytest 9.1.1.

Note this affects master too — happy to split it into a separate PR if preferred.