docs(parsing): add package and symbol doc comments

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.

config/parsing/selector/parse.go

@@ -7,6 +7,9 @@ import (
 	xs "github.com/go-gost/x/selector"
 )
 
+// ParseChainSelector creates a chain-level selector from a SelectorConfig. If
+// cfg is nil it returns nil. Strategy defaults to round-robin when unrecognized
+// or unset.
 func ParseChainSelector(cfg *config.SelectorConfig) selector.Selector[chain.Chainer] {
 	if cfg == nil {
 		return nil
@@ -32,6 +35,9 @@ func ParseChainSelector(cfg *config.SelectorConfig) selector.Selector[chain.Chai
 	)
 }
 
+// ParseNodeSelector creates a node-level selector from a SelectorConfig. If
+// cfg is nil it returns nil. Supported strategies: round/rr, random/rand,
+// fifo/ha, hash, and parallel. Defaults to round-robin.
 func ParseNodeSelector(cfg *config.SelectorConfig) selector.Selector[*chain.Node] {
 	if cfg == nil {
 		return nil
@@ -60,6 +66,8 @@ func ParseNodeSelector(cfg *config.SelectorConfig) selector.Selector[*chain.Node
 	)
 }
 
+// DefaultNodeSelector returns a node selector using round-robin strategy with
+// default fail filter settings.
 func DefaultNodeSelector() selector.Selector[*chain.Node] {
 	return xs.NewSelector(
 		xs.RoundRobinStrategy[*chain.Node](),
@@ -68,6 +76,8 @@ func DefaultNodeSelector() selector.Selector[*chain.Node] {
 	)
 }
 
+// DefaultChainSelector returns a chain selector using round-robin strategy
+// with default fail filter settings.
 func DefaultChainSelector() selector.Selector[chain.Chainer] {
 	return xs.NewSelector(
 		xs.RoundRobinStrategy[chain.Chainer](),