feat: add Peak Signal-to-Noise Ratio (PSNR) to compression

[AliAlimohammadi]

Description

Adds a pure-Rust implementation of Peak Signal-to-Noise Ratio (PSNR), a standard metric for measuring the quality of a compressed or reconstructed image relative to its original.

First, the Mean Squared Error (MSE) is computed across all $n$ pixel values:

$$MSE = \frac{1}{n} \sum_{i=1}^{n} (o_i - c_i)^2$$

PSNR is then derived in decibels (dB) as:

$$PSNR = 20 \cdot \log_{10}\left(\frac{PIXEL_MAX}{\sqrt{MSE}}\right)$$

where $PIXEL_MAX = 255$ for an 8-bit image. Returns f64::INFINITY when the two images are identical ($MSE = 0$).

Reference: Peak signal-to-noise ratio — Wikipedia

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked CONTRIBUTING.md and my code follows its guidelines.

[AliAlimohammadi]

@siriak, this is ready to be merged.

Note: CI is currently failing due to pre-existing Clippy warnings in binary_count_trailing_zeros.rs, transposition.rs, and prime_check.rs that are unrelated to this PR. Happy to fix these in a separate commit if the maintainers prefer.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.06%. Comparing base (8673305) to head (4df7b7e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1028   +/-   ##
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  Coverage   96.05%   96.06%           
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  Files         387      388    +1     
  Lines       29420    29468   +48     
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+ Hits        28260    28308   +48     
  Misses       1160     1160           

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