[esp32] Add software OTA downgrade protection (#17315)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/components/md5/__init__.py

@@ -0,0 +1,9 @@
+from tests.testing_helpers import ComponentManifestOverride
+
+
+def override_manifest(manifest: ComponentManifestOverride) -> None:
+    # md5's to_code calls cg.add_define("USE_MD5"), which gates md5.h. C++ unit
+    # test builds that pull md5 in transitively (e.g. ota's host backend, which
+    # has an md5::MD5Digest member) need that define, otherwise md5.h compiles to
+    # nothing and the dependent headers fail to find md5::MD5Digest.
+    manifest.enable_codegen()