fix: bound external image adapter execution

[ryanfowler]

Summary

• apply one deadline to adapter execution and stdout collection
• stop and terminate adapters immediately when stdout exceeds the cap
• contain Windows adapters in a kill-on-close Job Object before execution begins
• add regressions for inherited stdout and capped output

Validation

• cargo fmt --check
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --locked --all-features --lib --bins
• focused external image adapter tests
• isolated Windows-specific cross-compilation check

Full-project Windows cross-compilation was blocked locally by missing Windows C headers required by zstd-sys.