Refactor e2e_eval function and add unit tests

[kevinlu1248]

This PR was copied from kevinlu1248#17, written by Sweep, and AI-powered junior developer.

Description

This PR refactors the e2e_eval function in tools/end2end/eval_end2end.py to make it more modular and adds unit tests in eval_end2end_tests.py. The e2e_eval function is quite large and complex, so it has been broken down into smaller, more manageable functions. Additionally, unit tests have been added to ensure the correctness of the code and make it easier to identify and fix bugs in the future.

Summary of Changes

• Extracted the code block that calculates the Intersection over Union (IoU) between two polygons into a new function named calculate_iou in tools/end2end/utils.py.
• Extracted the code block that calculates the edit distance between two strings into a new function named calculate_edit_distance in tools/end2end/utils.py.
• Extracted the code block that calculates the precision, recall, and fmeasure into a new function named calculate_metrics in tools/end2end/utils.py.
• Extracted the code block that handles the matching of ground truth and detected text into a new function named match_gt_and_dt in tools/end2end/utils.py.
• Added unit tests for the extracted functions in eval_end2end_tests.py.

Please review and merge this PR. Thank you!

Fixes #1.

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[shiyutang]

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