FetchOne Optional with bare initializer (#71)

Previously, `@FetchOne var authUser: AuthUser?`
would not work because it was using a `FetchOne`
initializer which did not create a query. This
change adds another overloaded initializer that
creates a `Select` statement limiting the results
to just 1.

Considerations:
- The statement does not provide a default
  ordering, so if there are multiple records, it
  will just return the first one.

Added some tests to cover the original failure.

Author: cstock123

Sources/SharingGRDBCore/FetchOne.swift

@@ -79,6 +79,22 @@ public struct FetchOne<Value: Sendable>: Sendable {
   ) {
     sharedReader = SharedReader(value: wrappedValue)
   }
+  
+  /// Initializes this property with a query that fetches a single row from a table.
+  ///
+  /// - Parameters:
+  ///   - wrappedValue: A default value to associate with this property.
+  ///   - database: The database to read from. A value of `nil` will use the default database
+  ///     (`@Dependency(\.defaultDatabase)`).
+  public init(
+    wrappedValue: sending Value,
+    database: (any DatabaseReader)? = nil
+  ) where Value: StructuredQueriesCore.Table,
+        Value.QueryOutput == Value
+  {
+    let statement = Value.all.selectStar().asSelect().limit(1)
+    self.init(wrappedValue: wrappedValue, statement, database: database)
+  }
 
   /// Initializes this property with a wrapped value.
   ///

Tests/SharingGRDBTests/FetchTests.swift

@@ -20,11 +20,23 @@ struct FetchTests {
     #expect(records == [Record(id: 2), Record(id: 3)])
   }
 
-  @Test func fetchCountWithQuery() async throws {
+  @Test func fetchOneCountWithQuery() async throws {
     @FetchOne(Record.where { $0.id > 1 }.count()) var recordsCount = 0
     try await Task.sleep(nanoseconds: 100_000_000)
     #expect(recordsCount == 2)
   }
+  
+  @Test func bareFetchOneOptional() async throws {
+    @FetchOne var record: Record?
+    try await Task.sleep(nanoseconds: 100_000_000)
+    #expect(record != nil)
+  }
+  
+  @Test func fetchOneOptionalWithQuery() async throws {
+    @FetchOne(#sql("SELECT * FROM records LIMIT 1")) var record: Record?
+    try await Task.sleep(nanoseconds: 100_000_000)
+    #expect(record != nil)
+  }
 }
 
 @Table