Preserve trailing slash in file spec for directory

This enhances consistency with the `/` meaning "start relative path from here on", which can now be used consistently in both the path and url.

src/File/FileSpec.cs

@@ -106,18 +106,22 @@ public FileSpec(string path, Uri? uri = null, string? etag = null, string? sha =
             Sha = sha;
             NewSha = sha;
 
-            if (!finalPath && uri != null &&
+            if (!finalPath && uri != null && !uri.AbsolutePath.EndsWith('/') &&
                 (path.EndsWith('\\') || path.EndsWith('/')))
             {
                 path = System.IO.Path.Combine(path, WithDefaultPath(uri!).Path);
             }
 
             // This will also normalize double slashes.
-            var parts = path.Split(new[] { '\\', '/' }, StringSplitOptions.RemoveEmptyEntries);
+            var parts = path.Split(['\\', '/'], StringSplitOptions.RemoveEmptyEntries);
             if (parts.Length > 0 && parts[0] == ".")
                 Path = string.Join('/', parts.Skip(1));
             else
                 Path = string.Join('/', parts);
+
+            // Preserve trailing slash if present, for consistency with url ending in /.
+            if (path.EndsWith('/') || path.EndsWith("\\"))
+                Path += "/";
         }
 
         public string Path { get; }

src/File/Program.cs

@@ -59,7 +59,7 @@ static async Task<int> Main(string[] args)
                 }
 
                 // Try to pair Uri+File to allow intuitive download>path mapping, such as 
-                // https://gitub.com/org/repo/docs/file.md docs/file.md
+                // https://gitub.com/org/repo/docs/file.md > docs/file.md
                 if (Uri.TryCreate(extraArgs[i], UriKind.Absolute, out var uri))
                 {
                     var next = i + 1;