fix(huffman): Handle edge cases and improve error handling

[jesper-olsen]

Description

This PR improves the robustness of the Huffman encoding implementation by properly handling edge cases that previously caused undefined behavior or panics.

Summary of changes:

• Changed HuffmanDictionary::new() to return Option<Self> for safer API design
• Added proper handling for empty alphabets (returns None instead of panicking)
• Added special case handling for single-symbol alphabets, which previously failed during tree construction
• Improved error handling in decode() by replacing unwrap() calls with ? operator
• Added #[inline(always)] optimization for the frequently-called get_bit() method
• Added comprehensive documentation with usage examples
• Added tests for edge cases (empty and single-symbol inputs)

The Huffman encoding algorithm is a well-known lossless data compression algorithm. More details: https://en.wikipedia.org/wiki/Huffman_coding

Note: During development, I observed intermittent heap corruption errors in the test suite that occur even without these changes, suggesting pre-existing issues in the codebase.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I ran bellow commands using the latest version of rust nightly.
• 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.

Please make sure that if there is a test that takes too long to run ( > 300ms), you #[ignore] that or
try to optimize your code or make the test easier to run. We have this rule because we have hundreds of
tests to run; If each one of them took 300ms, we would have to wait for a long time.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.95833% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.33%. Comparing base (f2a23e9) to head (d64d56d).

Files with missing lines	Patch %	Lines
src/general/huffman_encoding.rs	98.95%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #912      +/-   ##
==========================================
+ Coverage   95.32%   95.33%   +0.01%     
==========================================
  Files         319      319              
  Lines       20807    20890      +83     
==========================================
+ Hits        19834    19916      +82     
- Misses        973      974       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[vil02]

The change looks good. One minor thing below.