feat(core): add TEMPEST_START constant (#791)

Author: innocenzi

src/Tempest/Core/src/Kernel.php

@@ -39,6 +39,8 @@ public static function boot(
         array $discoveryLocations = [],
         ?Container $container = null,
     ): self {
+        define('TEMPEST_START', value: hrtime(true));
+
         return (new self(
             root: $root,
             discoveryLocations: $discoveryLocations,

tests/Integration/Core/KernelTest.php

@@ -34,4 +34,14 @@ public function test_discovery_boot(): void
         $this->assertInstanceOf(TestDependency::class, $test);
         $this->assertSame('test', $test->input);
     }
+
+    public function test_kernel_start(): void
+    {
+        Kernel::boot(
+            root: getcwd(),
+            discoveryLocations: [],
+        );
+
+        $this->assertTrue(defined('TEMPEST_START'));
+    }
 }