[chore]Make get_field_attr safe and improve control flow in ts_core.py

[dardevelin]

Refactor get_field_attr in library.py and improve control flow in ts_core.py

Changes:

1. Refactor get_field_attr in library.py:

• Ensure safety using list slicing to avoid IndexError.
• Use any to determine if there is a value before using it.
• Use .get() for dictionary access to handle default cases and prevent KeyError.

2. Improve control flow in ts_core.py:

• Remove nesting by exiting early in match_conditions.
• Eliminate the need for try-catch blocks for better readability and control flow.

Additional Fix:

• Included fix for non-merged pull request #318.

Note:

• Kept existing_fields case unchanged due to add_field_to_entry's procedural nature.