Add RemoveAll extension for ICollection<T>

[Copilot]

ICollection<T> has no RemoveAll — only List<T> does. This adds the missing extension so any ICollection<T> implementation can remove elements by predicate.

Changes

• CollectionExtensions.cs — RemoveAll(Func<T, bool> predicate) on ICollection<T>: snapshots via ToArray() then removes matched items
• CollectionExtensionsTests.cs — basic coverage

ICollection<int> collection = new List<int> { 1, 2, 3, 4, 5 };
collection.RemoveAll(x => x % 2 == 0);
// collection == [1, 3, 5]

[Copilot]

Pull request overview

Adds a missing RemoveAll convenience for ICollection<T> so callers aren’t forced to cast to List<T> (or re-implement the pattern) when removing items by predicate.

Changes:

• Introduces ICollection<T>.RemoveAll(Func<T, bool>) extension that snapshots the collection and removes matching elements.
• Adds an initial unit test covering basic predicate-based removal.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
PowerKit/Extensions/CollectionExtensions.cs	Adds the new RemoveAll extension for ICollection<T>.
PowerKit.Tests/CollectionExtensionsTests.cs	Adds basic test coverage for the new extension.

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[Tyrrrz]

@copilot add test assert for RemoveAll return value

[Copilot]

@copilot add test assert for RemoveAll return value

Done in aac5c5d — the test now captures the return value and asserts it equals 2.