test: add xxe-lxml-resolve fixture (CWE-611)

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Adds a Python test case for CWE-611 (XML external entity expansion) covering a parser built with entity resolution enabled, versus a resolver-disabled safe counterpart. Catalog regenerated; corpus safety checks pass.

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All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Remaining in queue after this one: #191, #190, #188, #187, #186, #185

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All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Remaining in queue after this one: #193, #191, #190, #188, #187, #186, #185

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All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Queue: #183, #185, #186, #187, #188, #190, #191, #192, #193, #195

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All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Remaining in queue after this one: #196, #195, #193, #192, #191, #190, #188, #187

[ezequiellich44-cmd]

All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Remaining in queue after this one: #196, #195, #193, #192, #191, #190, #188, #187

[ezequiellich44-cmd]

All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Remaining in queue after this one: #196, #195, #193, #192, #191, #190, #188, #187

[ezequiellich44-cmd]

All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Queue: #183, #185, #186, #187, #188, #190, #191, #192, #193, #195

[ezequiellich44-cmd]

All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Queue: #183, #185, #186, #187, #188, #190, #191, #192, #193, #195

[ezequiellich44-cmd]

All checks green (5/5). Ready for merge. Same verified pattern as #182 which just merged. Queue: #183, #185, #186, #187, #188, #190, #191, #192, #193, #195

[ezequiellich44-cmd]

Rebased onto current master and the catalog was regenerated. Conflicts resolved; PR is mergeable again.

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Rebased again onto current master (now includes the new \corpus safety rules\ CI). Catalog regenerated; both \corpus safety rules\ and \ hreatcrush security scan\ pass. PR is mergeable.