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.
Prevent data loss and nil panics across 5 parse functions:
- chain: nil-guard hop entries to avoid deref on empty YAML lists
- hop: build merged metadata map instead of writing inherited values
into the original NodeConfig; swap+restore around ParseNode call
- node: use local connCfg/dialCfg instead of overwriting cfg.Connector
and cfg.Dialer fields; only fill in Type when empty
- parser: preserve existing config file fields when env vars override
Level/Addr (was replacing the entire struct)
- router: only update ipNet from dst CIDR if parse succeeds, keeping
the route.Net fallback instead of overwriting with nil
ginuerzh