Reuse compiled workspace exclusion patterns

[zanieb]

Workspace discovery normalized, escaped, and recompiled every exclusion glob for every candidate member, multiplying work in large workspaces with long exclusion lists.

Centralize exclusion matching, initialize it only when a candidate needs checking, and reuse patterns already compiled while parsing pyproject.toml. Patterns that require normalization or absolute matching retain their existing behavior, including parent-directory exclusions and workspace roots containing glob characters.

Optimized microbenchmark with 512 members and nonmatching exclusions:

Exclusions	Before	After	Improvement
64	168 ms	35 ms	4.8×
128	311 ms	126 ms	2.5×
256	934 ms	267 ms	3.5×
512	2,497 ms	683 ms	3.7×

[astral-automations-bot]

Promoted to #20988.