Restore Benchmark Functionality & Improve FileTree GetAllDescendantFiles

[Sewer56]

Associated details in the following Issues:

• Current Implementation of GetAllDescendentFiles is Slow  #22
• Missing Original Benchmarks for NexusMods.Paths from NexusMods.App  #21

Benchmarks:

(On 110476 files)

| Method                 | Mean      | Error     | StdDev    | Gen0     | Gen1    | Gen2    | Allocated |
|----------------------- |----------:|----------:|----------:|---------:|--------:|--------:|----------:|
| GetDescendants         |  3.532 ms | 0.0678 ms | 0.0635 ms |  74.2188 | 31.2500 | 31.2500 |   2.57 MB |
| OriginalGetDescendants | 16.972 ms | 0.3383 ms | 0.4154 ms | 562.5000 | 31.2500 | 31.2500 |  10.47 MB |

The improved GetAllDescendentFiles is a stripped down version of some code I wrote for Advanced Installer backend; figured I'd backport it.

Note: The benchmark code is copied 1:1 verbatim from the App repo, no review is needed there.

[codecov-commenter]

Codecov Report

Patch coverage is 50.00% of modified lines.

Files Changed	Coverage
src/NexusMods.Paths/FileTree/FileTreeNode.cs	50.00%

📢 Thoughts on this report? Let us know!.

[halgari]

This change makes the code non-lazy, and removes the ability to early terminate. This means on large file systes we're allocating a list of 300,000 items instead of streaming them into the processing function one at a time

[Al12rs]

The branch needs updating after main changes, apart from that should Seweryn add a lazy version back in or can this be merged?

[Sewer56]

We discussed about this last week during standup. This should be fine for merging with the API change as-is. If we ever run into a need to add a lazy method, we'll just restore it (but faster).