Refactor unit initialization and update dependencies

[olbrich]

Refactor the unit initialization for better clarity and structure. Additionally, update the Gemfile to include new dependencies and ensure compatibility with existing gems.

Rationale

Breaking Change: Hash Parameter Validation

The hash initialization API now strictly validates parameters:

# Previously accepted (might fail later or produce unexpected results)
RubyUnits::Unit.new(scalar: "invalid", numerator: "<meter>", denominator: "<second>")

# Now raises immediately
# ArgumentError: :scalar must be numeric
# ArgumentError: :numerator must be an Array<String>
# ArgumentError: :denominator must be an Array<String>

This is a breaking API change because:

1. Code that passed invalid types will now fail with ArgumentError
2. The failure happens earlier and with different error messages
3. Even if this was unintentional usage, changing error behavior is a breaking change

Non-Breaking Changes (would be MINOR/PATCH)

All other changes are backward compatible:

• ✅ Cache pollution prevention (bugfix)
• ✅ Regex optimization (performance improvement)
• ✅ Special format detection (internal improvement)
• ✅ Code refactoring (internal structure)