Fix/thread safety sendable (#146)

- Replace DateFormatter with modern Date.ParseStrategy for thread-safe RFC 2822 parsing
- Add Sendable conformance to FileManagerHandler per coding guidelines
- Fix async test in DataSourceTests to properly await Task execution
- Add comprehensive test coverage for invalid RFC 2822 date formats

Resolves #134, #135, #136, #137

🤖 Generated with [Claude Code](https://claude.ai/code)

Author: leogdion

Sources/BushelUtilities/Extensions/Date+RFC2822.swift

@@ -30,30 +30,32 @@
 public import Foundation
 
 extension Date {
-  /// RFC 2822 date formatter for HTTP Last-Modified headers
+  /// RFC 2822 parse strategy for HTTP Last-Modified headers
   ///
-  /// Shared static formatter for thread-safe, efficient date parsing.
+  /// Thread-safe parse strategy using modern Swift FormatStyle API.
   /// Format: "EEE, dd MMM yyyy HH:mm:ss zzz"
-  private static let rfc2822Formatter: DateFormatter = {
-    let formatter = DateFormatter()
-    formatter.dateFormat = "EEE, dd MMM yyyy HH:mm:ss zzz"
-    formatter.locale = Locale(identifier: "en_US_POSIX")
-    formatter.timeZone = TimeZone(secondsFromGMT: 0)
-    return formatter
-  }()
+  private static let rfc2822ParseStrategy = Date.ParseStrategy(
+    format:
+      // swiftlint:disable:next line_length
+      "\(weekday: .abbreviated), \(day: .twoDigits) \(month: .abbreviated) \(year: .padded(4)) \(hour: .twoDigits(clock: .twentyFourHour, hourCycle: .zeroBased)):\(minute: .twoDigits):\(second: .twoDigits) GMT",
+    locale: Locale(identifier: "en_US_POSIX"),
+    timeZone: TimeZone(secondsFromGMT: 0) ?? .gmt
+  )
 
   /// Creates a date from an RFC 2822 formatted string
   ///
   /// This initializer is designed for HTTP Last-Modified headers and similar RFC 2822 date formats.
+  /// Uses modern thread-safe ParseStrategy API for parsing.
   ///
   /// Example: "Fri, 19 Dec 2025 10:30:45 GMT"
   ///
   /// - Parameter rfc2822String: The RFC 2822 formatted date string
   /// - Returns: A date if parsing succeeds, nil otherwise
   public init?(rfc2822String: String) {
-    guard let date = Self.rfc2822Formatter.date(from: rfc2822String) else {
+    do {
+      self = try Self.rfc2822ParseStrategy.parse(rfc2822String)
+    } catch {
       return nil
     }
-    self = date
   }
 }

Sources/BushelUtilities/FileManager/FileManagerHandler.swift

@@ -34,7 +34,7 @@ public import Foundation
 #endif
 
 /// A struct that provides a wrapper around FileManager for file-related operations.
-public struct FileManagerHandler: FileHandler {
+public struct FileManagerHandler: FileHandler, Sendable {
   /// A closure that provides a `FileManager` instance.
   private let fileManager: @Sendable () -> FileManager
 

Tests/BushelFoundationTests/DataSourceTests.swift

@@ -82,11 +82,11 @@ internal final class DataSourceTests: XCTestCase {
     }
   }
 
-  internal func testSendable() {
+  internal func testSendable() async {
     // Compile-time check that DataSource is Sendable
-    Task {
+    await Task {
       let source = DataSource.appleDB
       XCTAssertEqual(source.rawValue, "appledb.dev")
-    }
+    }.value
   }
 }

Tests/BushelFoundationTests/FormattersTests.swift

@@ -128,6 +128,36 @@ internal final class FormattersTests: XCTestCase {
     )
   }
 
+  internal func testLastModifiedDateFormatterInvalidInputs() {
+    let sut = Formatters.lastModifiedDateFormatter
+
+    let invalidInputs = [
+      "",  // Empty string
+      "Not a date",  // Completely invalid
+      "32 Dec 2025 10:30:45 GMT",  // Invalid day
+      "Fri, 19 Foo 2025 10:30:45 GMT",  // Invalid month
+      "Fri, 19 Dec 2025 25:00:00 GMT",  // Invalid hour
+      "19 Dec 2025 10:30:45 GMT",  // Missing day name
+      "Fri, 19 Dec 2025 10:30:45",  // Missing timezone
+      "Fri, 00 Dec 2025 10:30:45 GMT",  // Invalid day (0)
+      "Fri, 19 Dec 2025 24:30:45 GMT",  // Invalid hour (24)
+      "Fri, 19 Dec 2025 10:60:45 GMT",  // Invalid minute
+      "Fri, 19 Dec 2025 10:30:60 GMT",  // Invalid second
+      "Fri, 19 Dec abcd 10:30:45 GMT",  // Invalid year
+      "Xyz, 19 Dec 2025 10:30:45 GMT",  // Invalid day name
+      "Fri, 19 Dec 2025 xx:30:45 GMT",  // Invalid hour format
+      "Fri, 19 Dec 2025 10:xx:45 GMT",  // Invalid minute format
+      "Fri, 19 Dec 2025 10:30:xx GMT",  // Invalid second format
+    ]
+
+    for input in invalidInputs {
+      XCTAssertNil(
+        sut.date(from: input),
+        "Should return nil for invalid input: \(input)"
+      )
+    }
+  }
+
   // MARK: - FormatStyle Tests
 
   internal func testFormatDate() {