feat: add SHA-1 hash function implementation

[AliAlimohammadi]

Description

Adds a pure-Rust implementation of the SHA-1 cryptographic hash function, producing a 160-bit (20-byte) digest from an arbitrary-length byte slice.

SHA-1 is specified in NIST FIPS 180-4. The implementation follows the spec directly:

1. Padding — appends 0x80, zero bytes, and the 64-bit big-endian message length so the total length is a multiple of 512 bits.
2. Message schedule — expands 16 big-endian words per block to 80 via ROTL₁(wₜ₋₃ ⊕ wₜ₋₈ ⊕ wₜ₋₁₄ ⊕ wₜ₋₁₆).
3. Compression — 80 rounds across four 20-round stages, each with its own mixing function (Ch, Parity, Maj) and round constant.
4. Serialisation — five 32-bit state words written back as big-endian bytes.

⚠️ SHA-1 is cryptographically broken and should not be used for security-sensitive purposes. This implementation is provided for educational and algorithmic completeness only.

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.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.92473% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.06%. Comparing base (1c7738e) to head (56e6709).

Files with missing lines	Patch %	Lines
src/ciphers/sha1.rs	98.92%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1030   +/-   ##
=======================================
  Coverage   96.06%   96.06%           
=======================================
  Files         388      389    +1     
  Lines       29468    29561   +93     
=======================================
+ Hits        28309    28399   +90     
- Misses       1159     1162    +3     

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[AliAlimohammadi]

@siriak, this is ready to be merged.