Add grammatical-case-aware TimeSpan humanization

readme.md

@@ -33,6 +33,13 @@ var precise = TimeSpan.FromMilliseconds(1500).HumanizeWithFractionalSeconds(
 Console.WriteLine(text); // 2 minutes
 Console.WriteLine(indianNumber); // one hundred crore
 Console.WriteLine(precise); // 1.5 seconds
+
+var german = CultureInfo.GetCultureInfo("de-DE");
+var duration = TimeSpan.FromDays(7).HumanizeWithCase(
+    GrammaticalCase.Dative,
+    culture: german);
+
+Console.WriteLine($"in {duration}"); // in einer Woche
 ```
 
 In v4 previews, applications can provide the exact noun forms for a culture's
@@ -54,6 +61,12 @@ it does not guess localized morphology or fall back to English. See
 [inflection and quantities](https://humanizr.net/docs/scenarios/inflection-and-quantities/)
 for the exact-form and lemmatization contracts.
 
+`HumanizeWithCase` returns only the duration phrase; add any required
+preposition yourself. Singular forms may include a locale-authored one-word
+or article, and a locale may encode a count in the unit form. Locales and custom
+components without verified case support throw `NotSupportedException`
+instead of falling back to English.
+
 ## Documentation
 
 - [Start using Humanizer](https://humanizr.net/docs/start/overview/)

src/Humanizer.SourceGenerators/Common/CanonicalLocaleAuthoring.cs

@@ -41,6 +41,7 @@ internal static class CanonicalLocaleAuthoring
         [
             "list",
             "formatter",
+            "durationCases",
             "phrases",
             "number",
             "ordinal",
@@ -146,6 +147,7 @@ internal static LocaleDefinition ToLocaleDefinition(CanonicalLocaleDocument docu
                         foreach (var propertyName in new[]
                         {
                             "pluralRule",
+                            "casePluralRule",
                             "dataUnitPluralRule",
                             "dataUnitNonIntegralForm",
                             "prepositionMode",
@@ -166,6 +168,10 @@ internal static LocaleDefinition ToLocaleDefinition(CanonicalLocaleDocument docu
 
                         break;
 
+                    case "durationCases":
+                        features["durationCases"] = surfaceMapping;
+                        break;
+
                     case "phrases":
                         features["phrases"] = surfaceMapping;
                         break;
@@ -544,6 +550,7 @@ public static class LegacyLocaleMigration
             "collectionFormatter",
             "dateOnlyToOrdinalWords",
             "dateToOrdinalWords",
+            "durationCases",
             "formatter",
             "grammar",
             "headings",
@@ -592,6 +599,7 @@ public static string ConvertToCanonicalYaml(string localeCode, string fileText)
 
             builder.AppendLine();
             builder.AppendLine("surfaces:");
+            AppendMigratedSurface(builder, "durationCases", root, "durationCases");
             AppendMigratedSurface(builder, "list", root, "collectionFormatter", isCollectionFormatter: true);
             AppendMigratedFormatterSurface(builder, root);
             AppendMigratedPhrasesSurface(builder, root);