Add godoc comments for all 62 exported symbols across 20 files in config/parsing/: 23 MDKey constants, 35 Parse*/List/Default* functions, 3 TLS helpers, 1 Args struct with 7 fields, and the package doc.
Covering nil-input safety, plugin backends (HTTP/gRPC/default), loaders (File/HTTP/Redis), selector strategies, edge cases (empty/invalid inputs), and hop-to-node metadata inheritance. All tests passing.
ginuerzh