Tests: map regex with location captures.

[Aayush7352]

Summary

Regression test for nginx/nginx#1573 / nginx/nginx#244: map variable with regex must not overwrite request capture state ($1, $2, ...) set by location regex.

What the test covers

• map with ~/.+$ regex pattern + regex location with captures → $1, $2 have correct values
• Verify captures work correctly for different URI lengths
• Verify captures work correctly for short URIs
• Verify normal location (no regex captures) unaffected
• Verify captures work when map variable is present in the response body

Verified

All 5 subtests pass with the fix from nginx/nginx#1573. Without the fix, 4/5 fail -- $1 and $2 are empty and Content-Length is over-counted.

Related: nginx/nginx#244, nginx/nginx#1573

[Aayush7352]

Updated companion test PR #82 adds further coverage for ticket #357 (map regex capture $1 in rewrite replacement).