test(imgproc): move histogram module tests into src/imgproc/tests.rs

[kalwalt]

Summary

Closes #111.

Every other imgproc submodule keeps its tests solely in the shared
src/imgproc/tests.rs, per the module structure convention in CLAUDE.md.
histogram.rs was the only one with its own embedded #[cfg(test)] mod tests block, left over from how #99 originally wrote it.

Mechanical move, no behavior change — all 33 histogram tests already went
through the public API with no dependency on private helpers, so they drop
straight into tests.rs's existing imgproc_tests module (which already
glob-imports crate::core::* and crate::imgproc::*) with no import
changes needed.

Test plan

• Same 342 lib test count before and after — nothing lost or duplicated.
• cargo test --workspace and cargo test --workspace --no-default-features --features std both pass.
• cargo fmt --check / clippy -D warnings clean under --all-features
  and --no-default-features.

🤖 Generated with Claude Code

[qodo-code-review]

PR Summary by Qodo

Relocate histogram tests into the shared imgproc test module

🧪 Tests 🕐 Less than 10 minutes

AI Description

• Consolidates 33 histogram tests in the shared imgproc test module.
• Exercises unchanged histogram behavior exclusively through public imgproc exports.
• Aligns histogram test organization with project module conventions.

Diagram

graph TD
  Runner["Cargo test"] --> Tests["Shared imgproc tests"] --> Api["Public imgproc API"] --> Histogram["Histogram implementation"]

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High-Level Assessment

The direct relocation is optimal because the tests already use only public APIs and the shared module supplies the required imports. Retaining an embedded test module would preserve the existing inconsistency, while converting these to integration tests would unnecessarily broaden this organizational change.

Files changed (2) +630 / -639

Tests (2) +630 / -639

histogram.rsRemove the embedded histogram test module +0/-639

Remove the embedded histogram test module

• Removes the module-local test block so the file contains only histogram production code. No histogram implementation or public API behavior changes.

src/imgproc/histogram.rs

tests.rsCentralize histogram tests in the imgproc test suite +630/-0

Centralize histogram tests in the imgproc test suite

• Moves the existing histogram tests into the shared imgproc test module. Coverage remains focused on public APIs for histogram calculation, back projection, comparison, equalization, and CLAHE.

src/imgproc/tests.rs

[qodo-code-review]

Code Review by Qodo

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