IsAnagram bug (per element counts)

### Describe the bug
The `IsAnagram` function is not checking per-element counts. It is only checking if they have the same elements, but not if the count of each element matches.

A more appropriate name for the current logic is something like `ContainsNoDifferingElements` or `IntersectsMatch` rather than `IsAnagram`. I would recommend changing the name or the logic of the method.

> Note: If you aren't going to check per-element counts, then you should also get rid of this check in `IsAnagrams`:
> ```cs
> if (source.Length != other.Length)
> return false;
> ```
> because length doesn't matter if you don't also check per-element counts.

### To Reproduce
Add the following case to the `IsAnagram` unit tests:
```cs
string aab = "aab";
string abb = "abb";
Assert.False(Permutations.IsAnargram(aab, abb));
```

### Expected behavior
Spans of the same length and elements but different per-element counts should not be considered re-orders/anagrams of each other.

### Environment:
_master branch_

### Additional context
I have written my own version of this algorithm in C# _(that fixes this issue)_ if interested here...
> Source Code: https://github.com/ZacharyPatten/Towel/blob/d2660e208ad3a44ab22f192834760c5b93dc82ac/Sources/Towel/Statics-SequenceAnalysis.cs#L1321
> Examples: https://github.com/ZacharyPatten/Towel/blob/d2660e208ad3a44ab22f192834760c5b93dc82ac/Examples/BasicsAndExtensions/Program.cs#L406
> Testing: https://github.com/ZacharyPatten/Towel/blob/d2660e208ad3a44ab22f192834760c5b93dc82ac/Tools/Towel_Testing/Statics.cs#L2086
> _Note: `MapHashLinked` is my version of a `Dictionary` if you look at the source code._

El problema está en el método Permutations.IsAnagram. Consulta las pruebas unitarias para entender el comportamiento actual. El error es que no comprueba las cantidades de cada elemento. La solución consiste en actualizar el algoritmo para contar las apariciones de cada carácter. El enlace externo proporcionado muestra una implementación corregida. Añade primero el caso de prueba que falla y, después, modifica el método para que lo supere.

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