Add ApplyJetStreamConfigChanges to ConfigReloader for detecting MaxMemoryStore,
MaxFileStore, and Domain changes during hot reload. Add Domain property to
JetStreamOptions. Port 10 unit tests covering all change permutations.
Adds ClusterConfigChangeResult and ApplyClusterConfigChanges to ConfigReloader,
comparing route/gateway/leaf URL sets between old and new NatsOptions and reporting
added/removed routes for connection reconciliation on hot reload.
Add PropagateAuthChanges to ConfigReloader that compares Users, Accounts,
and Authorization token between old and new NatsOptions, returning an
AuthChangeResult describing which auth fields changed for connection re-evaluation.
E6: Add IsSystemAccount property to Account, mark $SYS account as system,
add IsSystemSubject/IsSubscriptionAllowed/GetSubListForSubject helpers to
route $SYS.> subjects to the system account's SubList and block non-system
accounts from subscribing.
E7: Add ConfigReloader.ReloadAsync and ApplyDiff for structured async reload,
add ConfigReloadResult/ConfigApplyResult types. SIGHUP handler already wired
via PosixSignalRegistration in HandleSignals.
E8: Add PropagateAuthChanges to re-evaluate connected clients after auth
config reload, disconnecting clients whose credentials no longer pass
authentication with -ERR 'Authorization Violation'.
Adds OptsGoParityTests.cs with 49 tests porting 15 unmapped Go test
functions from server/opts_test.go: random port semantics, listen port
config variants, multiple users, authorization block parsing, options
defaults (TestDefaultSentinel), write_deadline parsing, path handling,
variable/env-var substitution chains, and unknown field tolerance.
