Fix ParseKwargs crash on a --model-kwargs value containing '=' or a non-literal - #2758

What

ParseKwargs (used by --model-kwargs / --opt-kwargs in the train/validate scripts) crashes on some valid inputs:

$ python -c "import argparse; from timm.utils.misc import ParseKwargs; \
  p=argparse.ArgumentParser(); p.add_argument('--model-kwargs', nargs='*', default={}, action=ParseKwargs); \
  print(p.parse_args(['--model-kwargs','note=size=large']))"
ValueError: too many values to unpack (expected 2)

Two issues in the same spot:

1. key, value = value.split('=') splits on every =, so any value containing an = (e.g. note=size=large, or a URL with a query string) raises too many values to unpack.
2. The literal_eval fallback only catches ValueError. A value that isn't a valid Python literal but is invalid syntax (like size=large) raises SyntaxError, which isn't caught, so it crashes instead of falling back to a string.

Fix

• Split on the first = only (split('=', 1)).
• Catch SyntaxError as well as ValueError in the string fallback.

Both are minimal and the only key=value parser in the tree (grep confirms misc.py:29 is the sole .split('=')).

After

note=size=large            -> {'note': 'size=large'}
url=http://h/p?a=1&b=2     -> {'url': 'http://h/p?a=1&b=2'}
depth=12 act=nn.GELU       -> {'depth': 12, 'act': 'nn.GELU'}
cfg={"a": 1}               -> {'cfg': {'a': 1}}

Existing literal parsing (ints, floats, bools, dicts) is unchanged.

Tests

Added tests/test_utils.py covering literal values, a value containing =, and the non-literal string fallback. The note=size=large case fails on main (both bugs) and passes here.