fix(decorators): avoid mutating original function metadata on functools.wraps - #729

Problem

As reported in #728, decorating a wrapper created with \unctools.wraps\ using \SetParseFn\ or \SetParseFns\ unexpectedly mutates how the original wrapped function parses its arguments. Because \unctools.wraps\ copies the function's attribute dictionary, the underlying Fire metadata dictionary is shared, and updating it in place affects both wrapper and wrapped functions.

Solution

• In _SetMetadata, create a shallow copy of the metadata dictionary before assigning the new attribute, ensuring the target function receives its own distinct metadata map.
• In \SetParseFn\ and \SetParseFns, create a fresh \parse_fns\ mapping with a copied
  amed\ dictionary so updates to named parsers do not mutate shared dictionaries in place.
• Add regression unit tests in \ire/decorators_test.py\ verifying that wrapping a function decorated with \SetParseFns\ / \SetParseFn\ preserves independent parser behavior on both the original and wrapped functions.

Fixes #728.