fix: dispose SHA1 instance in Caching.hashString; use SHA1.HashData on .NET 5+

On netstandard2.0, SHA1.Create() returns a HashAlgorithm (IDisposable)
that was never disposed — a small but genuine resource leak.

On .NET 5+, use the static SHA1.HashData(byte[]) method which avoids
creating a disposable instance entirely and is the idiomatic modern API.
On netstandard2.0, wrap the instance in 'use' to ensure deterministic
disposal.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/FSharp.Data.Runtime.Utilities/Caching.fs

@@ -55,7 +55,15 @@ let createInMemoryCache (expiration: TimeSpan) =
 /// Get hash code of a string - used to determine cache file
 let private hashString (plainText: string) =
     let plainTextBytes = Encoding.UTF8.GetBytes(plainText)
-    let hashBytes = SHA1.Create().ComputeHash(plainTextBytes)
+
+    let hashBytes =
+#if NET5_0_OR_GREATER
+        SHA1.HashData(plainTextBytes)
+#else
+        use sha1 = SHA1.Create()
+        sha1.ComputeHash(plainTextBytes)
+#endif
+
     let s = Convert.ToBase64String(hashBytes)
     s.Replace("ab", "abab").Replace("\\", "ab")