fix(perf): rebuild cached integration plans containing null function refs

[bpamiri]

Closes #3457.

On Lucee 7 the cached component-integration plan (#3236) can come back with a function reference resolved to Java null — e.g. when the plan was first built while the engine was still compiling the mixin component. $integrateFunctions then copies the null into every materialized model/controller/mapper instance, and Lucee throws a bare NullPointerException (no stack) when it later enumerates the component. The failure is flaky and cleared by a reload, which rebuilds the plan.

• $buildComponentIntegrationPlan no longer caches null refs (skips + logs a one-time warning).
• $componentIntegrationPlan validates the cached plan once per request (request-scope struct flag — dotted request-scope keys don't round-trip on RustCFML) and rebuilds it in place when poisoned.
• New IntegrationPlanSpec (global area): fresh plans contain no null refs, poisoned entries are detected, and a poisoned cached plan is rebuilt.

Verification

• Local Lucee 7: global 242 pass, model 991 pass, wheelstest 255 pass, 0 fail.
• Local RustCFML full suite: 5549 pass, only the known baseline migrationSpec :: addIndex failure — no new failures vs tools/rustcfml/baseline.json.
• Full local Lucee suite run in progress at time of opening.