feat: add config processor mapping parsed config to NatsOptions

Port of Go server/opts.go processConfigFileLine switch. Maps parsed
NATS config dictionaries to NatsOptions fields including:
- Core options (port, host, server_name, limits, ping, write_deadline)
- Logging (debug, trace, logfile, log rotation)
- Authorization (single user, users array with permissions)
- TLS (cert/key/ca, verify, pinned_certs, handshake_first)
- Monitoring (http_port, https_port, http/https listen, base_path)
- Lifecycle (lame_duck_duration/grace_period)
- Server tags, file paths, system account options

Includes error collection (not fail-fast), duration parsing (ms/s/m/h
strings and numeric seconds), host:port listen parsing, and 56 tests
covering all config sections plus validation edge cases.

tests/NATS.Server.Tests/TestData/basic.conf

@@ -0,0 +1,19 @@
+port: 4222
+host: "0.0.0.0"
+server_name: "test-server"
+max_payload: 2mb
+max_connections: 1000
+debug: true
+trace: false
+logtime: true
+logtime_utc: false
+ping_interval: "30s"
+ping_max: 3
+write_deadline: "5s"
+max_subs: 100
+max_sub_tokens: 16
+max_control_line: 2048
+max_pending: 32mb
+lame_duck_duration: "60s"
+lame_duck_grace_period: "5s"
+http_port: 8222