Make smart rule exclusion cover rule chains of any depth

[CoolOppo]

Resolves the TODO in generate_children. The exclusion previously
skipped a rule only when the output file matched exactly the same rule
set as the input, which recognizes re-application just one level deep.
Deeper chains (a.js -> a.min.js -> a.pkg.min.js) re-applied earlier
rules to derived files, and configs whose rules match their own outputs
(e.g. a lone *.js -> *.min.js rule without an exclude) expanded the
file graph without bound until the walker overflowed its stack.

A rule is now also skipped when the input path already matches the
shape of the rule's to template (capture group references treated as
wildcards): such a file already looks like one of the rule's outputs,
so the rule was already applied somewhere along the chain that produced
it. Every file of a chain is checked against the output shapes of all
of its matching rules, so the exclusion composes across chains of any
depth. The TODO suggested recursing on the rule-set comparison instead,
but no signature recursion can work: a genuine source file and a deep
derivative produce identical signature sequences, so only the shape of
the name itself can tell them apart.

The old rule-set comparison is kept as a fallback for to templates
that rewrite only part of a path, where the anchored output shape never
matches. Rules that rewrite a file in-place are now exempt from both
checks: they are stored as self-loops and cannot grow a chain, and the
old comparison used to silently drop them whenever any other rule
matched the same file.

Co-Authored-By: Claude noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01MxcgW5UDkTmh1iB7xKPDdc

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