refactor: implement context managers for deterministic file resource cleanup

[28ananthaprakash]

Proposed changes:
This PR refactors file I/O operations across utility scripts and test suites to ensure safe resource management.

Scope of Changes

• Context Managers: Replaced manual open()/close() calls with Python context managers (with statements). This ensures file descriptors are automatically closed even if exceptions occur during execution, preventing potential resource leaks.
• Path Handling: Updated test fixtures in test_convert_featurizer.py to utilize pathlib objects (tmp_path) rather than manual string manipulation and file creation. This improves test harness readability and cross-platform compatibility.
• Error Handling: Mitigated potential OSError risks in pattern_utils.py by ensuring the file handle is scoped correctly within the try/except block.

Motivation
Leaving file handles open relies on the garbage collector for cleanup, which is non-deterministic. Explicit context management is strictly required for long-running processes (like model training) to avoid hitting system file limits.

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)