Expose source path on LogFileInterface

Add LogFileInterface::getPath(): ?string so detectors can dispatch on a
filename hint when the original path is known. Default implementation on
the abstract LogFile base returns null; PathLogFile records its
constructor argument. StringLogFile and StreamLogFile inherit the null
default. Tests cover both the path and null-fallback cases.

test/tests/Log/File/PathLogFileTest.php

@@ -14,4 +14,12 @@ class PathLogFileTest extends TestCase
 
         $this->assertStringEqualsFile($path, $logFile->getContent());
     }
+
+    public function testGetPathReturnsConstructorArgument(): void
+    {
+        $path = __DIR__ . "/../../../data/simple.log";
+        $logFile = new PathLogFile($path);
+
+        $this->assertSame($path, $logFile->getPath());
+    }
 }