fix(ipynb): catch decoding exceptions in accepts() to prevent pipeline crashes on non-decodable application/json files

[aoright]

Description

Fixes #1894.

When converting files whose MIME type starts with application/json but contain non-ASCII/binary data (such as a French PDF containing UTF-8 characters that failed to decode using the system's default locale/ASCII codec, or other binary files), IpynbConverter.accepts() raises a UnicodeDecodeError or ValueError which propagates uncaught and crashes the entire conversion pipeline.

This PR wraps the decode() operation in IpynbConverter.accepts() inside a try/except (UnicodeDecodeError, ValueError, LookupError) block, returning False gracefully when the file is not decodable, instead of raising an exception.

Verification

• Added a new unit test test_ipynb_converter_accepts_handling_decode_error to packages/markitdown/tests/test_module_misc.py.
• Verified that the unit tests pass.

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