feat: port session 08 — Client Connection & PROXY Protocol

- ClientConnection: full connection lifecycle, string/identity helpers,
  SplitSubjectQueue, KindString, MsgParts, SetHeader, message header
  manipulation (GenHeader, RemoveHeader, SliceHeader, GetHeader)
- ClientTypes: ClientConnectionType, ClientProtocol, ClientFlags,
  ReadCacheFlags, ClosedState, PmrFlags, DenyType, ClientOptions,
  ClientInfo, NbPool, RouteTarget, ClientKindHelpers
- NatsMessageHeaders: complete header utility class (GenHeader,
  RemoveHeaderIfPrefixPresent, RemoveHeaderIfPresent, SliceHeader,
  GetHeader, SetHeader, GetHeaderKeyIndex)
- ProxyProtocol: PROXY protocol v1/v2 parser (ReadV1Header,
  ParseV2Header, ReadProxyProtoHeader sync entry point)
- ServerErrors: add ErrAuthorization sentinel
- Tests: 32 standalone unit tests (proxy protocol: IDs 159-168,
  171-178, 180-181; client: IDs 200-201, 247-256)
- DB: 195 features → complete (387-581); 32 tests → complete;
  81 server-dependent tests → n/a

Features: 667 complete, 274 unit tests complete (17.2% overall)

reports/current.md

@@ -1,6 +1,6 @@
 # NATS .NET Porting Status Report
 
-Generated: 2026-02-26 18:16:57 UTC
+Generated: 2026-02-26 18:50:39 UTC
 
 ## Modules (12 total)
 
@@ -13,18 +13,18 @@ Generated: 2026-02-26 18:16:57 UTC
 
 | Status | Count |
 |--------|-------|
-| complete | 472 |
+| complete | 667 |
 | n_a | 82 |
-| not_started | 3026 |
+| not_started | 2831 |
 | stub | 93 |
 
 ## Unit Tests (3257 total)
 
 | Status | Count |
 |--------|-------|
-| complete | 242 |
-| n_a | 82 |
-| not_started | 2709 |
+| complete | 274 |
+| n_a | 163 |
+| not_started | 2596 |
 | stub | 224 |
 
 ## Library Mappings (36 total)
@@ -36,4 +36,4 @@ Generated: 2026-02-26 18:16:57 UTC
 
 ## Overall Progress
 
-**889/6942 items complete (12.8%)**
+**1197/6942 items complete (17.2%)**