Fixes #22640
Fixes #22641

• Nested map support. (Table[string, Table[string, string]])
• Negative enum support (where abs value of ordinal clashed with other value).

Summary by cubic

Adds nested map support and fixes enum handling for negative numeric values in the Nim client codegen to generate correct types and valid enum names. Fixes #22640 and #22641.

• Bug Fixes
  • Resolve $ref in getTypeDeclaration to detect nested maps/arrays and emit correct Table[...] types.
  • Detect numeric enums from integer/number schemas and prefix negative values with "Neg" to avoid identifier collisions.
  • Update petstore fixtures and generated Nim models (DigestEmailFrequency, PetStatistics) to cover these cases.

^{Written for commit c81ac9e. Summary will update on new commits.}