Previously BuildDefaultTLSConfig generated a new random self-signed
certificate in memory on every run, making it impossible for users to
extract and trust the certificate in their system trust store.
Now when no explicit cert files are configured, GOST:
1. First checks cert.pem / key.pem in CWD (backward compatible)
2. Then checks auto-ca-cert.pem / auto-ca-key.pem under $HOME/.gost/
3. If none found, generates a new ECDSA P-256 CA certificate, persists
it to $HOME/.gost/, and uses it
The persisted cert has IsCA=true so tools recognize it as a root CA.
Falls back to in-memory-only when disk writes fail.
Closesgo-gost/gost#876
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.
ginuerzh