simplify builds and deps - replace LibGit2Sharp with GitCore

In the past, we had used LibGit2Sharp to clone Git repositories and read their commits and files.
That often worked, but the native dependencies of such a solution have caused [many](ba6abfc) [problems](1c7d3e4).
This commit resolves these problems by switching to an implementation of Git without such complicated dependencies.

Author: Viir

implement/GitCore/Common/EnumerableExtensions.cs

@@ -0,0 +1,91 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+
+namespace GitCore.Common;
+
+/// <summary>
+/// Extension methods for <see cref="IEnumerable{T}"/>.
+/// </summary>
+public static class EnumerableExtensions
+{
+    /// <summary>
+    /// Creates an <see cref="IEqualityComparer{T}"/> for sequences of <see cref="IComparable"/> elements.
+    /// </summary>
+    /// <typeparam name="T">The type of the enumerable, which must implement <see cref="IEnumerable{IComparable}"/>.</typeparam>
+    /// <returns>An <see cref="IEqualityComparer{T}"/> that compares sequences element by element.</returns>
+    public static IEqualityComparer<T> EqualityComparer<T>() where T : IEnumerable<IComparable> =>
+        new IEnumerableEqualityComparer<T>();
+
+    /// <summary>
+    /// Creates an <see cref="IComparer{T}"/> for sequences of <see cref="IComparable"/> elements.
+    /// </summary>
+    /// <typeparam name="T">The type of the enumerable, which must implement <see cref="IEnumerable{IComparable}"/>.</typeparam>
+    /// <returns>An <see cref="IComparer{T}"/> that compares sequences element by element.</returns>
+    public static IComparer<T> Comparer<T>() where T : IEnumerable<IComparable> => new IEnumerableComparer<T>();
+
+    private class IEnumerableEqualityComparer<T> : IEqualityComparer<T> where T : IEnumerable<IComparable>
+    {
+        public bool Equals(T? x, T? y)
+        {
+            if (ReferenceEquals(x, y))
+                return true;
+
+            if (x is null || y is null)
+            {
+                return false;
+            }
+
+            return x.SequenceEqual(y);
+        }
+
+        public int GetHashCode(T obj) => 0;
+    }
+
+    private class IEnumerableComparer<T> : IComparer<T> where T : IEnumerable<IComparable>
+    {
+        public static int Compare([AllowNull] IEnumerable<IComparable> x, [AllowNull] IEnumerable<IComparable> y)
+        {
+            if (ReferenceEquals(x, y))
+                return 0;
+
+            if (x is null)
+                return -1;
+
+            if (y is null)
+                return 1;
+
+            if (x.Equals(y))
+                return 0;
+
+            var xEnumerator = x.GetEnumerator();
+            var yEnumerator = y.GetEnumerator();
+
+            while (true)
+            {
+                var xHasCurrent = xEnumerator.MoveNext();
+                var yHasCurrent = yEnumerator.MoveNext();
+
+                if (!xHasCurrent && !yHasCurrent)
+                    return 0;
+
+                if (!xHasCurrent)
+                    return -1;
+
+                if (!yHasCurrent)
+                    return 1;
+
+                var currentComparison = xEnumerator.Current.CompareTo(yEnumerator.Current);
+
+                if (currentComparison is not 0)
+                    return currentComparison;
+            }
+        }
+
+        public int Compare(T? x, T? y)
+        {
+            return IEnumerableComparer<T>.Compare(x, y);
+        }
+    }
+}

implement/GitCore/GitCore.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="SharpZipLib" Version="1.4.2" />
+    <PackageReference Include="System.IO.Compression" Version="4.3.0" />
+  </ItemGroup>
+
+</Project>