🏷️(vitest) No intermediate var to declare our types (#5766)

**Description**

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We used to rely on the typing of an intermediate variable to declare the
typings of `FastCheckItBuilder`. We dropped it to drop some unwanted
usages of the directive: `eslint-disable-next-line
@typescript-eslint/no-unused-vars`.

Related to #5282.

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.changeset/large-shoes-divide.md

@@ -0,0 +1,5 @@
+---
+"@fast-check/vitest": minor
+---
+
+🏷️(vitest) No intermediate var to declare our types

packages/vitest/src/internals/TestBuilder.ts

@@ -20,16 +20,6 @@ type TestPropRecord<Ts, TsParameters extends Ts = Ts> = (
   params?: FcParameters<TsParameters>,
 ) => (testName: string, prop: PropRecord<Ts>, timeout?: number) => void;
 
-/**
- * prop has just been declared for typing reasons, ideally TestProp should be enough
- * and should be used to replace `{ prop: typeof prop }` by `{ prop: TestProp<???> }`
- */
-// eslint-disable-next-line @typescript-eslint/no-unused-vars
-declare const prop: <Ts, TsParameters extends Ts = Ts>(
-  arbitraries: Ts extends [any] | any[] ? ArbitraryTuple<Ts> : ArbitraryRecord<Ts>,
-  params?: FcParameters<TsParameters>,
-) => (testName: string, prop: Ts extends [any] | any[] ? Prop<Ts> : PropRecord<Ts>, timeout?: number) => void;
-
 function adaptParametersForRecord<Ts>(
   parameters: FcParameters<[Ts]>,
   originalParamaters: FcParameters<Ts>,
@@ -124,7 +114,14 @@ function buildTestProp<Ts extends [any] | any[], TsParameters extends Ts = Ts>(
  * Revamped {it,test} with added `.prop`
  */
 export type FastCheckItBuilder<T> = T &
-  ('each' extends keyof T ? T & { prop: typeof prop } : T) & {
+  ('each' extends keyof T
+    ? T & {
+        prop: <Ts, TsParameters extends Ts = Ts>(
+          arbitraries: Ts extends [any] | any[] ? ArbitraryTuple<Ts> : ArbitraryRecord<Ts>,
+          params?: FcParameters<TsParameters>,
+        ) => (testName: string, prop: Ts extends [any] | any[] ? Prop<Ts> : PropRecord<Ts>, timeout?: number) => void;
+      }
+    : T) & {
     [K in keyof Omit<T, 'each'>]: FastCheckItBuilder<T[K]>;
   };