Add micro-benchmark to jpeg code and clean up test separation

[mcroomp]

Add benchmark for the critical encoding and decoding of coefficients.

Best practice is to keep test code in a separate module so that all the imports are isolated.

Moved rstest to a test dependency

Moved to single implementation of read_file for testing

[Copilot]

Pull Request Overview

This PR adds micro-benchmarks for JPEG coefficient encoding/decoding and improves test code organization by centralizing test utilities and separating test dependencies.

• Adds new micro-benchmarks for block-level JPEG encoding and decoding operations
• Consolidates the read_file function into a single implementation in lib.rs
• Moves rstest from a runtime dependency to a test-only dependency

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/end_to_end.rs	Removes duplicate read_file function and uses centralized version
lib/src/structs/lepton_file_writer.rs	Moves test code into proper test module and uses centralized utilities
lib/src/structs/lepton_file_reader.rs	Removes duplicate read_file function and reorganizes test code
lib/src/micro_benchmark.rs	Adds exports for new block-level benchmarks
lib/src/lib.rs	Adds centralized read_file function for testing/benchmarking
lib/src/jpeg/jpeg_write.rs	Reorganizes test code and adds new block encoding benchmark
lib/src/jpeg/jpeg_read.rs	Reorganizes test code and adds new block decoding benchmark
lib/src/jpeg/jpeg_header.rs	Expands visibility of utility functions for benchmarking
lib/src/jpeg/bit_writer.rs	Adds clear method and reorganizes test code
lib/src/jpeg/bit_reader.rs	Reorganizes test code into proper module
dll/src/lib.rs	Moves test code into proper module and uses centralized utilities
dll/Cargo.toml	Moves rstest to dev-dependencies
benches/benches.rs	Uses centralized read_file function and adds new benchmarks

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[Copilot]

Pull Request Overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

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[Copilot]

Creating an empty Vec and then trying to reserve memory is less efficient than directly creating a Vec with capacity. Consider using Vec::with_capacity(encoded_length) or handle the allocation error at creation time.

Suggested change

	let mut data_buffer = Vec::new();
	if let Err(e) = data_buffer.try_reserve_exact(encoded_length) {
	return err_exit_code(
	ExitCode::OutOfMemory,
	format!(
	"unable to allocate {} bytes for jpeg output buffer: {:?}",
	encoded_length, e
	),
	);
	}
	let mut data_buffer = Vec::with_capacity(encoded_length);

[Copilot]

The constructor now takes ownership of a Vec but doesn't validate or document expectations about the buffer state (e.g., should it be empty, can it contain existing data). Consider documenting the expected buffer state or adding validation.

[Copilot]

[nitpick] The black_box import is only used in benchmark code but is imported at the top of a function scope. Consider moving this import closer to its usage or document why it's needed for the benchmark.