Do not warn on references to in-scope PEP 695 type parameters

[apoorvdarshan]

Fixes #14462

Problem

References to PEP 695 type parameters — in type parameter bounds, argument lists, return annotations, and the bodies of generic classes — are converted into py:class pending cross-references. Type parameters have no link target and, per PEP 695 scoping, shadow any documented object of the same name, so every such reference produces a spurious reference target not found warning under -n (the reporter counts ~1000 in an 8k LoC project). Reproduced on master with the issue's snippet (3 spurious warnings).

Fix

• PyObject.handle_signature() records the type parameter names introduced by a signature in env.ref_context['py:type_params'] (saving the enclosing scope on the directive instance), so they are visible while parsing the type parameter list itself (bounds/constraints/defaults), the argument list, and the return annotation.
• PyObject.after_content() restores the enclosing scope, so the names also cover the object's body — e.g. py:method:: eggs(arg: int) -> T inside py:class:: Spam[T] — and never leak past the directive (mirrors the existing py:class/py:module ref-context handling, including nesting).
• type_to_xref() renders an in-scope, un-dotted name as plain Text instead of a pending_xref. Rendered output is unchanged — an unresolvable reference already fell back to plain text — but no warning is emitted, and a documented class shadowed by a type parameter is no longer (incorrectly) linked.

Out-of-scope references still warn: py:function:: outside(x: T) after a generic class continues to report T.

Two existing doctree-shape tests (test_class_def_pep_695, test_class_def_pep_696) pinned the old behavior of in-scope names inside bounds/constraints (e.g. S: Sequence[T]) being pending xrefs; they were updated to expect plain text for exactly those names (Sequence, tuple, int etc. remain xrefs).

This is complementary to #14504, which handles the autodoc/runtime-TypeVar side via missing-reference; this PR covers the directive-syntax layer, where scope is known at parse time.

Verification

• New testroot test-domain-py-type-param-scope + test_pep_695_type_param_scope_nitpicky (asserts the only remaining warning is the genuinely out-of-scope T) and test_pep_695_type_params_render_as_text — both fail on master.
• Full test suite (minus test_intl): ~2,900 passed, failure set byte-identical to master in my environment (6 pre-existing environment-dependent failures).
• ruff check/ruff format clean on changed files; mypy clean on both changed modules.

AI policy disclosure

Per the AI policy: this contribution was prepared with the assistance of an AI tool (Claude Code), used for the investigation, the patch, and the tests. I reproduced the issue, reviewed and verified the change and all test results, and take responsibility for the contribution — I'll respond to review feedback personally.