Add Timer.recordNanoseconds Generic Overload (#28) (#30)

Motivation:

As discussed in Issue #28, there are a few preferred lightweight APIs for getting timestamps such as `DispatchTime` but those APIs return `UInt64` types, which need to be handled for overflow.

Modifications:

Added a generic `BinaryInteger` overload method for `recordNanoseconds` that guards against accidental overflows from `UInt64` to `Int64`

Result:

Users now have access to a new method to record nanosecond measurements with `Timer` that guards against overflows.

Sources/CoreMetrics/Metrics.swift

@@ -267,6 +267,15 @@ public class Timer {
         self.handler.recordNanoseconds(duration)
     }
 
+    /// Record a duration in nanoseconds.
+    ///
+    /// - parameters:
+    ///     - value: Duration to record.
+    @inlinable
+    public func recordNanoseconds<DataType: BinaryInteger>(_ duration: DataType) {
+        self.recordNanoseconds(duration >= Int64.max ? Int64.max : Int64(duration))
+    }
+
     /// Record a duration in microseconds.
     ///
     /// - parameters:

Sources/Metrics/Metrics.swift

@@ -52,7 +52,7 @@ public extension Timer {
     func record(_ duration: DispatchTimeInterval) {
         switch duration {
         case .nanoseconds(let value):
-            self.recordNanoseconds(Int64(value))
+            self.recordNanoseconds(value)
         case .microseconds(let value):
             self.recordMicroseconds(value)
         case .milliseconds(let value):

Tests/MetricsTests/CoreMetricsTests.swift

@@ -224,18 +224,22 @@ class MetricsTests: XCTestCase {
         // run the test
         let timer = Timer(label: "test-timer")
         let testTimer = timer.handler as! TestTimer
-        // micro
-        timer.recordMicroseconds(UInt64.max)
+        // nano
+        timer.recordNanoseconds(UInt64.max)
         XCTAssertEqual(testTimer.values.count, 1, "expected number of entries to match")
         XCTAssertEqual(testTimer.values[0].1, Int64.max, "expected value to match")
-        // milli
-        timer.recordMilliseconds(UInt64.max)
+        // micro
+        timer.recordMicroseconds(UInt64.max)
         XCTAssertEqual(testTimer.values.count, 2, "expected number of entries to match")
         XCTAssertEqual(testTimer.values[1].1, Int64.max, "expected value to match")
-        // seconds
-        timer.recordSeconds(UInt64.max)
+        // milli
+        timer.recordMilliseconds(UInt64.max)
         XCTAssertEqual(testTimer.values.count, 3, "expected number of entries to match")
         XCTAssertEqual(testTimer.values[2].1, Int64.max, "expected value to match")
+        // seconds
+        timer.recordSeconds(UInt64.max)
+        XCTAssertEqual(testTimer.values.count, 4, "expected number of entries to match")
+        XCTAssertEqual(testTimer.values[3].1, Int64.max, "expected value to match")
     }
 
     func testGauge() throws {