FallBackward: ICollection<> implementation

[viceroypenguin]

This PR adds an ICollection<> implementation of the Fallback operator.

Fixes #370

// * Summary *

BenchmarkDotNet=v0.13.5, OS=Windows 11 (10.0.22621.1555/22H2/2022Update/SunValley2)
12th Gen Intel Core i7-12700H, 1 CPU, 20 logical and 14 physical cores
.NET SDK=8.0.100-preview.3.23178.7
  [Host] : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2

Method	source	N	Mean	Error	StdDev	Gen0	Gen1	Allocated
FillBackwardCount	Syste(...)nt32] [47]	10000	13.57 ns	0.169 ns	0.150 ns	0.0032	0.0000	40 B
FillBackwardCount	Syste(...)rator [36]	10000	80,539.61 ns	569.023 ns	532.265 ns	-	-	376 B
FillBackwardCopyTo	Syste(...)nt32] [47]	10000	20,054.10 ns	173.320 ns	153.643 ns	3.1738	0.0305	40064 B
FillBackwardCopyTo	Syste(...)rator [36]	10000	95,658.32 ns	497.560 ns	465.418 ns	3.1738	0.1221	40400 B

Code

#load "BenchmarkDotNet"

void Main()
{
	RunBenchmark();
}

public IEnumerable<object[]> EnumerableArguments()
{
	foreach (var i in new[] { 10_000, })
	{
		yield return new object[] { Enumerable.Range(1, i), i, };
		yield return new object[] { Enumerable.Range(1, i).ToList(), i, };
	}
}

[Benchmark]
[ArgumentsSource(nameof(EnumerableArguments))]
public void FillBackwardCount(IEnumerable<int> source, int N)
{
	_ = source.FillBackward(e => e % 10 != 5).Count();
}

[Benchmark]
[ArgumentsSource(nameof(EnumerableArguments))]
public void FillBackwardCopyTo(IEnumerable<int> source, int N)
{
	var arr = new int[N];
	_ = source.FillBackward(e => e % 10 != 5).CopyTo(arr);
}

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.05 🎉

Comparison is base (b5de5aa) 87.26% compared to head (bcb7617) 87.32%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #371      +/-   ##
==========================================
+ Coverage   87.26%   87.32%   +0.05%     
==========================================
  Files         239      239              
  Lines        7098     7123      +25     
  Branches     1650     1657       +7     
==========================================
+ Hits         6194     6220      +26     
+ Misses        464      463       -1     
  Partials      440      440              

Impacted Files	Coverage Δ
Source/SuperLinq/FillBackward.cs	98.00% <100.00%> (+2.00%)	⬆️

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.