Add LZW and Arithmetic Coding algorithms in compression category

[enqneres]

Description

This pull request adds two classic lossless compression algorithms to the compression category:

LZW (Lempel–Ziv–Welch)

Builds a dictionary of strings and replaces repeating patterns with shorter codes.

Example:

Input: TOBEORNOTTOBEORTOBEORNOT
Output: [84, 79, 66, 69, 79, 82, 78, 79, 84, 256, 258, 260, 265, 259, 261, 263]

Arithmetic Coding

Encodes a message as a single number between 0 and 1 using symbol probabilities.

Example:

Input: "BABA" (A:0.5, B:0.5)
Output: 0.34375

Files added:

src/main/java/com/thealgorithms/compression/LZW.java

src/main/java/com/thealgorithms/compression/ArithmeticCoding.java

📚 Related issue: #6798

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 36 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.68%. Comparing base (6b7d201) to head (fc2ea6c).

Files with missing lines	Patch %	Lines
...om/thealgorithms/compression/ArithmeticCoding.java	0.00%	18 Missing ⚠️
...c/main/java/com/thealgorithms/compression/LZW.java	0.00%	18 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## master #6803 +/- ## ============================================ - Coverage 77.82% 77.68% -0.15%  + Complexity 6392 6390 -2  ============================================ Files 732 734 +2 Lines 21320 21356 +36 Branches 4182 4189 +7 ============================================ - Hits 16592 16590 -2  - Misses 4059 4095 +36  - Partials 669 671 +2 

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[enqneres]

Anyone to approve my PR? Have I completed all the steps or am I missing any?