feat: Add Codable conformance (#6)

* Add Codable conformance

Author: hassila

Sources/Histogram/Histogram.swift

@@ -16,7 +16,7 @@ import Numerics
 /**
  * Number of significant digits for values recorded in histogram.
  */
-public enum SignificantDigits: Int8 {
+public enum SignificantDigits: Int8, Codable {
     case zero, one, two, three, four, five
 }
 
@@ -51,7 +51,7 @@ public enum HistogramOutputFormat {
  * they are encountered. Note that recording calls that cause auto-resizing may take longer to execute, as resizing
  * incurs allocation and copying of internal data structures.
  */
-public struct Histogram<Count: FixedWidthInteger> {
+public struct Histogram<Count: FixedWidthInteger & Codable>: Codable {
     /// The lowest value that can be discerned (distinguished from 0) by the histogram.
     public let lowestDiscernibleValue: UInt64
 

Tests/HistogramTests/HistogramAutosizingTests.swift

@@ -65,7 +65,7 @@ final class HistogramAutosizingTests: XCTestCase {
 
     func testAutoSizingAdd() throws {
         var histogram1 = Histogram<UInt64>(numberOfSignificantValueDigits: .two)
-        var histogram2 = Histogram<UInt64>(numberOfSignificantValueDigits: .two)
+    //    let histogram2 = Histogram<UInt64>(numberOfSignificantValueDigits: .two)
 
         histogram1.record(1_000)
         histogram1.record(1_000_000_000)
@@ -74,8 +74,8 @@ final class HistogramAutosizingTests: XCTestCase {
         throw XCTSkip("Histogram.add() is not implemented yet")
         //histogram2.add(histogram1)
 
-        XCTAssert(histogram2.valuesAreEquivalent(histogram2.max, 1_000_000_000),
-                  "Max should be equivalent to 1_000_000_000")
+   //     XCTAssert(histogram2.valuesAreEquivalent(histogram2.max, 1_000_000_000),
+   //               "Max should be equivalent to 1_000_000_000")
     }
 
     func testAutoSizingAcrossContinuousRange() {