[Sim] guard malformed expression parsing

[Harmenszoon]

Summary

• Guard pet.any.active expression parsing so malformed pet.any no longer reads past the split-vector bounds.
• Guard actors.<name>.<expr> expression parsing against missing actors by checking the looked-up actor pointer instead of the sim target.

Details

Both changes route malformed expressions through the normal invalid-expression initialization error path instead of undefined behavior or an access violation.

pet.any.active.<trailing> is also no longer silently accepted as pet.any.active; the valid generated form remains pet.any.active.

Validation

• Rebuilt build-codex with VS2022 DevCmd + CMake.
• simc hunter=test spec=beast_mastery level=90 race=orc role=attack position=ranged_back load_default_gear=1 load_default_talents=1 iterations=1 output=NUL actions=variable,name=bad,value=pet.any now exits 30 with a normal initialization error.
• Same command with value=pet.any.active exits 0.
• Same command with value=actors.nope.health.pct now exits 30 with a normal initialization error instead of access violation.
• Same command with value=actors.test.health.pct exits 0.
• simc display_build=2 output=NUL exits 0.
• simc profiles/CI.simc iterations=1 cleanup_threads=1 output=NUL exits 0 with existing baseline profile/data warnings.
• git diff --check origin/midnight...HEAD passed.