Documented callable parameter structure for Assert::callback()

`Assert::callback()` accepts a `$callable` that, **AT MOST**, accepts **1** parameter and
returns `bool`.

The number of times I've written `->with(self::callback(function ($a, $b, $c) : void {`
is very high:

 * I generally forget that `->with()` is variadic (that's OK)
 * I forget that `self::callback()` applies to a single parameter
 * I forget that the `callable` must return a `bool` in order to operate

In order to avoid these mistakes, the `Callback` constraint is now templated, and the
given `callable` is enforced to require at most one parameter, and to always return
`bool`.

As a counter-example to verify that this type signature works, I've run this against
`tests/static-analysis/TestUsingCallbacks.php` with following snippet:

```php
    public function testInvalid(): void
    {
        $mock = $this->createMock(SayHello::class);

        $mock
            ->expects(self::once())
            ->method('hey')
            ->with(self::callback(static function (string $a, string $b): bool {
                return true;
            }))
            ->willReturn('Hey Joe!');

        self::assertSame('Hey Joe!', $mock->hey('Joe'));
    }
```

The above now raises:

```
ERROR: InvalidArgument - tests/static-analysis/TestUsingCallbacks.php:62:35 - Argument 1 of PHPUnit\StaticAnalysis\TestUsingCallbacks::callback expects callable(mixed):bool, pure-Closure(string, string):true provided (see https://psalm.dev/004)
            ->with(self::callback(static function (string $a, string $b): bool {
                return true;
            }))
```

This produces

src/Framework/Assert.php

@@ -3114,6 +3114,13 @@ public static function isTrue(): IsTrue
         return new IsTrue;
     }
 
+    /**
+     * @psalm-template CallbackInput of mixed
+     *
+     * @psalm-param callable(mixed $callback): bool $callback
+     *
+     * @psalm-return Callback<CallbackInput>
+     */
     public static function callback(callable $callback): Callback
     {
         return new Callback($callback);

src/Framework/Constraint/Callback.php

@@ -9,18 +9,21 @@
  */
 namespace PHPUnit\Framework\Constraint;
 
-use function call_user_func;
-
 /**
  * Constraint that evaluates against a specified closure.
+ *
+ * @psalm-template CallbackInput of mixed
  */
 final class Callback extends Constraint
 {
     /**
      * @var callable
+     *
+     * @psalm-var callable(CallbackInput $input): bool
      */
     private $callback;
 
+    /** @psalm-param callable(CallbackInput $input): bool $callback */
     public function __construct(callable $callback)
     {
         $this->callback = $callback;
@@ -39,9 +42,11 @@ public function toString(): string
      * constraint is met, false otherwise.
      *
      * @param mixed $other value or object to evaluate
+     *
+     * @psalm-param CallbackInput $other
      */
     protected function matches($other): bool
     {
-        return call_user_func($this->callback, $other);
+        return ($this->callback)($other);
     }
 }

tests/static-analysis/TestUsingCallbacks.php

@@ -0,0 +1,54 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of PHPUnit.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace PHPUnit\StaticAnalysis;
+
+use PHPUnit\Framework\TestCase;
+
+/** @see https://www.youtube.com/watch?v=rXwMrBb2x1Q */
+interface SayHello
+{
+    public function hey(string $toPerson): string;
+}
+
+/** @small */
+final class TestUsingCallbacks extends TestCase
+{
+    public function testWillSayHelloAndCheckCallbackInput(): void
+    {
+        $mock = $this->createMock(SayHello::class);
+
+        $mock
+            ->expects(self::once())
+            ->method('hey')
+            ->with(self::callback(static function (string $input): bool {
+                self::assertStringContainsString('Joe', $input);
+
+                return true;
+            }))
+            ->willReturn('Hey Joe!');
+
+        self::assertSame('Hey Joe!', $mock->hey('Joe'));
+    }
+
+    public function testWillSayHelloAndCheckCallbackWithoutAnyInput(): void
+    {
+        $mock = $this->createMock(SayHello::class);
+
+        $mock
+            ->expects(self::once())
+            ->method('hey')
+            ->with(self::callback(static function (): bool {
+                return true;
+            }))
+            ->willReturn('Hey Joe!');
+
+        self::assertSame('Hey Joe!', $mock->hey('Joe'));
+    }
+}