fix: dataset inheritance with method chaining (beforeEach()->with(), describe()->with())

Fixes issue where datasets were not applied when using method chaining patterns
like beforeEach()->with([...]) or describe()->with([...]) inside nested describe blocks.

Root cause: Multiple functions were using Backtrace::file() which returns the
immediate caller's filename. This breaks when called through method chaining
because the backtrace returns internal Pest files instead of the test file.

Solution: Use Backtrace::testFile() which walks the entire backtrace to find
the actual test file being executed. This matches the pattern already used by
test() and describe() functions.

Changes in src/Functions.php:
- beforeEach(): Use testFile() to fix beforeEach()->with() pattern
- afterEach(): Use testFile() for consistency with beforeEach()
- beforeAll(): Use testFile() for better error messages
- afterAll(): Use testFile() for better error messages
- pest(): Use testFile() to fix pest()->beforeEach() pattern
- uses(): Use testFile() for consistency with pest()
- covers(): Use testFile() for correct test file context
- mutates(): Use testFile() for correct test file context

Changes in src/PendingCalls/DescribeCall.php:
- __destruct(): Force BeforeEachCall destructor before test creation
- __call(): Use $this->filename instead of Backtrace, more efficient
- __call(): Properly merge describing context for nested describe blocks

Fixes patterns:
- beforeEach()->with([...])
- describe()->with([...])
- pest()->beforeEach()->with([...]

Tests passing:
- tests/Features/Describe.php (all dataset tests)
- tests/Hooks/BeforeEachTest.php (global hook execution)
- tests/Features/Expect/toMatchSnapshot.php (28 tests)

src/PendingCalls/DescribeCall.php

@@ -5,7 +5,6 @@ declare(strict_types=1);
 namespace Pest\PendingCalls;
 
 use Closure;
-use Pest\Support\Backtrace;
 use Pest\Support\Description;
 use Pest\TestSuite;
 
@@ -53,7 +52,11 @@ final class DescribeCall
      */
     public function __destruct()
     {
-        unset($this->currentBeforeEachCall);
+        // Ensure BeforeEachCall destructs before creating tests
+        // by moving to local scope and clearing the reference
+        $beforeEach = $this->currentBeforeEachCall;
+        $this->currentBeforeEachCall = null;
+        unset($beforeEach);  // Trigger destructor immediately
 
         self::$describing[] = $this->description;
 
@@ -71,12 +74,13 @@ final class DescribeCall
      */
     public function __call(string $name, array $arguments): self
     {
-        $filename = Backtrace::file();
-
         if (! $this->currentBeforeEachCall instanceof \Pest\PendingCalls\BeforeEachCall) {
-            $this->currentBeforeEachCall = new BeforeEachCall(TestSuite::getInstance(), $filename);
+            $this->currentBeforeEachCall = new BeforeEachCall(TestSuite::getInstance(), $this->filename);
 
-            $this->currentBeforeEachCall->describing[] = $this->description;
+            $this->currentBeforeEachCall->describing = array_merge(
+                DescribeCall::describing(),
+                [$this->description]
+            );
         }
 
         $this->currentBeforeEachCall->{$name}(...$arguments);