Reject truncated payloads across all conversion paths

[Brian Caswell (demoray)]

Summary

Reject truncated payloads across all image conversion paths.

#883 identified that a LiME record could declare a larger range than its payload contained. `std::io::copy` returned the number of bytes copied, but the result was ignored, allowing conversion to succeed with zero-padded or incomplete output.

Reviewing the other conversion paths found the same issue in:

• LiME-to-raw conversion.
• Compressed AVML-to-LiME conversion.
• Compressed AVML-to-raw conversion.

Compressed records could also omit or provide an incorrect eight-byte compressed-length trailer. The readers previously skipped the trailer with `seek`, which can succeed beyond EOF.

Changes

• Require bounded copies to produce exactly the declared uncompressed size.
• Return `UnexpectedEof` when a LiME or compressed payload ends early.
• Read the existing compressed-length trailer instead of seeking over it.
• Validate that the trailer matches the number of compressed bytes consumed.
• Add regression tests covering truncated LiME payloads, truncated compressed payloads, missing trailers, and incorrect trailer values.

This does not change the LiME or compressed AVML wire formats. Valid existing images remain compatible; malformed images that were previously accepted now fail conversion.

Validation

• `cargo test --no-default-features --features convert`
• `cargo clippy --no-default-features --features convert --all-targets -- -D warnings`