fix: wrap all type-hint resolution errors in CodecError

[zza-830]

Problem

Codec.decode documents that it raises CodecError on any structural mismatch or conversion failure, but get_type_hints can also raise AttributeError (stale qualified references like "os.ThisDoesNotExist"), TypeError (malformed expressions like "1 + 'x'"), and SyntaxError (invalid annotations like "def f("). These escaped the CodecError contract.

Closes #38

Fix

Broaden the except clause from NameError to (NameError, AttributeError, TypeError, SyntaxError):

# Before
except NameError as err:

# After
except (NameError, AttributeError, TypeError, SyntaxError) as err:

Tests

Added two new test cases:

• test_decode_stale_qualified_ref_raises_codec_error — validates AttributeError wrapping
• test_decode_malformed_expression_raises_codec_error — validates SyntaxError wrapping

tests/serde/test_codec.py::test_decode_unresolvable_forward_ref_raises_codec_error PASSED
tests/serde/test_codec.py::test_decode_stale_qualified_ref_raises_codec_error PASSED
tests/serde/test_codec.py::test_decode_malformed_expression_raises_codec_error PASSED