[SCRIPT] Support PEP 695 symbolic variables in Relax and TIR

[tqchen]

Relax and TIR dependent type fields need symbolic integer variables to be declared in a function signature without persisting parser-only metadata in IR.

• Accept standard module-level TypeVar declarations on Python 3.10+ and bare or int-bound PEP 695 parameters on Python 3.12+.
• Treat declarations as syntax sugar for fresh int64 TIR variables used by dependent signature fields; unused declarations disappear and no function attrs, type-parameter fields, or runtime parameters are added.
• Parse both versioned forms through shared signature plumbing while retaining dialect-specific annotation and body handling.

Representative Python 3.12+ output uses PEP 695 and postponed annotations, so dependent expressions are unquoted:

from __future__ import annotations

@R.function(private=True)
def main[M](x: R.Tensor((M, M * 2), dtype="float32")):
    return x

Before Python 3.12, the portable output uses a module-level TypeVar and quotes compound dependent expressions:

M = TypeVar("M")

@R.function(private=True)
def main(x: R.Tensor((M, "M * 2"), dtype="float32")):
    return x

The same declaration and printing rules apply to TIR buffer signatures.

Validation:

• Latest-main native build completed successfully.
• Consolidated Relax and TIR TypeVar round-trip tests passed.
• Related Relax/TIR parser, printer, and well-formedness suites passed 661 tests with 4 expected failures.
• Touched-file pre-commit hooks and diff checks passed.
• The implementation does not change Relax well-formedness analysis.