fix(analyzer): stop quadratic backtracking in in_pan low pattern

[uwezkhan]

Change Description

in_pan_recognizer.py, PAN (Low) pattern, matched against a boundary-rich string with no four-digit run:

in_pan PAN (Low) regex, input = "a " repeated:
  length  25,000  ->   2.0 s
  length  50,000  ->   8.1 s
  length 100,000  ->  32.4 s   (larger input reaches REGEX_TIMEOUT_SECONDS)

Both lookaheads use .*?, so each one rescans the rest of the text at every word boundary and match time is quadratic in input length. IN_PAN is enabled by default for English, so this sits on the analyze path for any analyzed text.

Before: (?=.*?[a-zA-Z])(?=.*?[0-9]{4})[\w@#$%^?~-]{10}. . walks across non-token characters, so the lookahead scan is unbounded.

After: (?=[\w@#$%^?~-]*?[a-zA-Z])(?=[\w@#$%^?~-]*?[0-9]{4})[\w@#$%^?~-]{10}. The lookaheads only traverse the PAN token's own character class, so each stops at the first non-token character. Matching is linear (100 KB now ~9 ms) and every valid PAN whose four digits sit inside the token still matches at the same span and score.

Tradeoff: scoping the lookaheads also drops one previous match. A ten-letter token is no longer reported as a PAN when four digits happen to appear later in the text; a PAN's digits live inside the number, so that case was a false positive.

Issue reference

N/A

Checklist

• I have reviewed the contribution guidelines
• I have signed the CLA (if required)
• My code includes unit tests
• All unit tests and lint checks pass locally
• My PR contains documentation updates / additions if required

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR updates the India PAN low-confidence regex to avoid expensive scanning/backtracking behavior and adds regression tests to validate both correctness and runtime characteristics.

Changes:

• Refined the low-confidence PAN regex lookaheads to scope matching to the token character class.
• Added a regression test for low-confidence detection with embedded digits.
• Added a performance/regression test intended to catch quadratic-time behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
presidio-analyzer/presidio_analyzer/predefined_recognizers/country_specific/india/in_pan_recognizer.py	Adjusts the low-confidence PAN regex lookaheads to avoid scanning beyond the candidate token.
presidio-analyzer/tests/test_in_pan_recognizer.py	Adds functional + runtime regression tests for the updated low-confidence PAN regex.