MustHaveMinimumLength for immutable array

[feO2x]

Closes #121

Production Code

Throw.InvalidMinimumImmutableArrayLength.cs
Exception factory method that creates appropriate error messages for minimum length violations, handling both regular and default ImmutableArray instances.

Check.MustHaveMinimumLength.cs

Two extension method overloads:

• First overload: Takes parameterName and message parameters, throws InvalidCollectionCountException
• Second overload: Takes custom exception factory delegate for custom exceptions

Both methods use parameter.IsDefault check to safely handle default instances (treats as length 0).

[Copilot]

Pull Request Overview

This PR implements the MustHaveMinimumLength assertion for ImmutableArray<T> to avoid boxing that would occur with generic IEnumerable<T> extensions. The implementation includes proper handling of default immutable array instances and follows the existing library patterns.

• Adds exception factory method for minimum length violations with appropriate error messages
• Implements two extension method overloads following the library's standard pattern (default exception and custom exception factory)
• Includes comprehensive test coverage for all scenarios including edge cases with default instances

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

File	Description
issue-121-must-have-minimum-length-for-immutable-array.md	Planning document outlining implementation requirements
Throw.InvalidMinimumImmutableArrayLength.cs	Exception factory method for minimum length validation errors
Check.MustHaveMinimumLength.cs	Extension methods implementing the minimum length assertion
MustHaveMinimumLengthTests.cs	Comprehensive test suite covering all scenarios and edge cases