Detect equivalent numeric mapping keys (#26009)
## Summary
Mapping-pattern duplicate detection and F601 compare keys through
`HashableExpr`, but numeric normalization previously only recognized
values equivalent to `True` or `False`. This meant that other values
Python treats as the same dictionary key were considered distinct:
```python
match value:
case {2: first, 2.0: second}: ...
```
This adds a dedicated numeric representation for integer, float,
boolean, and complex literals so that exactly integral floats compare
with equivalent integers, including signed forms and zero-imaginary
complex values. Tuple normalization is limited to statically known
values so dynamic tuple elements do not introduce false-positive F601
diagnostics.
Numeric normalization uses the existing `u64` integer representation.
Larger integers retain structural comparison, avoiding
arbitrary-precision conversion in parser and linter hot paths.
