feat: add comprehensive temperature conversion function

[AliAlimohammadi]

Description

This PR adds comprehensive temperature conversion functionality supporting 8 major temperature scales using a clean, maintainable API design.

Design Approach

This implementation uses:

• A single convert_temperature(value, from, to) function
• A TemperatureUnit enum for type safety
• Kelvin as an intermediary for all conversions

Scales Supported

• Kelvin (K) - SI base unit
• Celsius (°C) - Standard metric scale
• Fahrenheit (°F) - Imperial scale
• Rankine (°R) - Absolute Fahrenheit
• Delisle (°De) - Historical inverted scale
• Newton (°N) - Isaac Newton's scale
• Réaumur (°Ré) - Historical European scale
• Rømer (°Rø) - Historical Danish scale

API Usage

use conversions::{convert_temperature, TemperatureUnit};

// Convert 100°C to Fahrenheit
let fahrenheit = convert_temperature(100.0, TemperatureUnit::Celsius, TemperatureUnit::Fahrenheit);
// Result: 212.0

// Convert 0K to Celsius
let celsius = convert_temperature(0.0, TemperatureUnit::Kelvin, TemperatureUnit::Celsius);
// Result: -273.15

Changes

• Added src/conversions/temperature.rs with:
  • TemperatureUnit enum
  • convert_temperature() function
  • Internal to_kelvin() and from_kelvin() methods
• Updated src/conversions/mod.rs to export the public API
• Comprehensive test coverage including:
  • Individual scale conversions
  • Round-trip validation for all 64 combinations
  • Special temperature points (absolute zero, water freezing/boiling)
  • Historical scale verification
  • Same-unit conversion (identity test)

Testing

• ✅ All unit tests pass
• ✅ Round-trip conversions verified for all 64 combinations
• ✅ Clippy warnings resolved
• ✅ Code formatted with cargo fmt
• ✅ No dead code warnings

References

• Temperature conversion formulas - Wikipedia
• All formulas verified against standard references

Checklist

• Code follows the project's style guidelines
• Tests added for new functionality
• Module documentation added
• All tests pass locally
• Code formatted with cargo fmt
• No clippy warnings
• Public API exported in mod.rs
• Type-safe enum-based design

[codecov-commenter]

Codecov Report

❌ Patch coverage is 99.21875% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.07%. Comparing base (4402903) to head (4f3e46b).

Files with missing lines	Patch %	Lines
src/conversions/temperature.rs	99.21%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1002      +/-   ##
==========================================
+ Coverage   96.06%   96.07%   +0.01%     
==========================================
  Files         371      372       +1     
  Lines       25943    26071     +128     
==========================================
+ Hits        24922    25048     +126     
- Misses       1021     1023       +2     

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[AliAlimohammadi]

@siriak, this is ready to be merged.