Measure CometRegex whitelist coverage on representative regex patterns

[sam-1112]

What is the problem the feature request solves?

The initial CometRegex whitelist introduced by PR #5415 is deliberately conservative. It rejects commonly used constructs such as ., ^, $, \d, \w, and \s.

We currently do not know what fraction of representative real-world rlike patterns is admitted for automatic native execution. TPC-DS does not contain useful rlike coverage, so it cannot answer this question.

Without an admission-rate measurement, it is difficult to prioritize follow-up compatibility work or estimate how much real-world workload coverage the whitelist provides.

Describe the potential solution

Identify one or more representative regex corpora, such as public SQL workloads, open-source application queries, or safely shareable production-derived patterns.

Run every literal pattern through CometRegex and report:

• the corpus source and collection method;
• total, admitted, and rejected pattern counts;
• the admission percentage;
• duplicate-handling methodology;
• rejection counts grouped by unsupported construct or analyzer rule;
• useful pattern-length and complexity distributions.

Use the results to prioritize follow-up work such as support for leading ^ or safe normalization of selected Java regex constructs.

The whitelist should not be weakened solely to increase the reported admission percentage.

Additional context

Follow-up from #5415 and #5351.

This tracks the representative admission-rate measurement requested during review of #5415: #5415 (review)

The original issue notes that the TPC query corpus does not contain rlike usage: #5351