feat(lambda-rs): Add write_slice and write_bytes to Buffer

[vmarcella]

Summary

Adds write_slice and write_bytes methods to Buffer in lambda-rs, providing more flexible ways to upload data to GPU buffers. These complement the existing write_value method by supporting raw byte slices and typed slices of plain-old-data values.

Related Issues

• Resolves [Feature] Add write_bytes and write_slice Methods to Buffer #80

Changes

• Added write_bytes(&self, gpu: &Gpu, offset: u64, data: &[u8]) for writing raw byte slices directly to a buffer
• Added write_slice<T: Copy>(&self, gpu: &Gpu, offset: u64, data: &[T]) for writing slices of POD values (vertices, indices, instance data, uniform blocks)
• Extracted value_as_bytes and slice_as_bytes helper functions to convert typed data to byte slices
• Refactored write_value to use the new write_bytes internally for consistency
• Added overflow protection in slice_as_bytes with a debug assertion for byte length overflow
• Added unit tests: value_as_bytes_matches_native_bytes, slice_as_bytes_matches_native_bytes, and slice_as_bytes_empty_is_empty

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• Feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (updates to docs, specs, tutorials, or comments)
• Refactor (code change that neither fixes a bug nor adds a feature)
• Performance (change that improves performance)
• Test (adding or updating tests)
• Build/CI (changes to build process or CI configuration)

Affected Crates

• lambda-rs
• lambda-rs-platform
• lambda-rs-args
• lambda-rs-logging
• Other:

Checklist

• Code follows the repository style guidelines (cargo +nightly fmt --all)
• Code passes clippy (cargo clippy --workspace --all-targets -- -D warnings)
• Tests pass (cargo test --workspace)
• New code includes appropriate documentation
• Public API changes are documented
• Breaking changes are noted in this PR description

Testing

Commands run:

cargo build --workspace
cargo test --workspace
cargo test -p lambda-rs -- --nocapture

Manual verification steps (if applicable):

1. Run unit tests to verify byte conversion correctness
2. Verify existing examples that use write_value continue to work

Screenshots/Recordings

N/A - No visual changes.

Platform Testing

• macOS
• Windows
• Linux

Additional Notes

• The T: Copy bound ensures only trivially copyable types can be written, which is required for safe byte reinterpretation
• The slice_as_bytes function includes overflow protection that returns an empty slice and triggers a debug assertion if the byte length calculation would overflow
• These methods are useful for uploading arrays of vertices, indices, instance transforms, or any other bulk data to GPU buffers

[Copilot]

Pull request overview

Adds higher-level buffer upload APIs to lambda-rs by introducing Buffer::write_bytes and Buffer::write_slice, and refactors write_value to use shared byte-conversion helpers with accompanying unit tests.

Changes:

• Added Buffer::write_bytes for uploading raw &[u8] directly to GPU buffers
• Added Buffer::write_slice<T> plus value_as_bytes / slice_as_bytes helpers for uploading typed data as bytes
• Added unit tests validating byte conversion for single values and slices (including empty slices)

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