perf: optimize literal classification and extend numeric literal support (#15934)

This PR optimizes literal recognition and improves `grind` support for
rational and signed fixed-width integer literals.

Replace value-extractor calls with direct Boolean checks. Add scientific
`Rat` recognition and `Int8`/`Int16`/`Int32`/`Int64` extraction and
normalization. Fix interpretation of aliased types and handling of
literals in match conditions. Add consistency tests covering wrapping,
boundaries, metadata, and metavariables.