[codex] fix image rendering edge cases

[ryanfowler]

Summary

• Prevent double EXIF orientation when images are decoded through external adapters.
• Bound external image adapter cleanup so timeout paths do not wait indefinitely on inherited stdout handles.
• Harden terminal image dimension math against overflow with extreme terminal sizes.
• Reduce block image ANSI output churn by tracking foreground/background state instead of resetting every cell.

Why

The image renderer had a few correctness and robustness edge cases: external decoders could return already-oriented pixels while fetch applied the original EXIF orientation again, adapter timeout cleanup could block if a descendant kept stdout open, and terminal sizing math used direct u32 multiplication. Block rendering was also emitting avoidable ANSI reset sequences per cell.

Validation

• cargo fmt --check
• cargo test --locked --all-features image::
• cargo test --locked --all-features --test terminal image
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --locked --all-features --lib --bins