Standardized gremlin-dotnet connection options

[GumpacG]

Standardize gremlin-dotnet connection options

Implements the .NET portion of the TinkerPop 4.x GLV connection-options standardization. Renames several ConnectionSettings properties and the Auth factory methods to canonical names (old names kept as [Obsolete] deprecated aliases), aligns defaults, adds new options, and fixes two latent bugs. .NET driver changes only; the other GLVs follow in separate PRs.

Proposal: https://lists.apache.org/thread/yqtr2wnb1kq2pqqq4002cz511q5o0bkg

Renames (deprecated aliases retained)

Old	New	Default
MaxConnectionsPerServer	MaxConnections	128
IdleConnectionTimeout	IdleTimeout	180s
ConnectionTimeout	ConnectTimeout	5s
KeepAliveInterval	KeepAliveTime	30s
EnableCompression	Compression	-
Auth.BasicAuth	Auth.Basic	-
Auth.SigV4Auth	Auth.Sigv4	-

The old property names and auth methods are retained as [Obsolete] deprecated aliases (marked "As of release 4.0.0, ...") that delegate to the canonical members, so existing code keeps compiling.

Behavior changes (breaking)

• ConnectTimeout default lowered 15s → 5s.
• KeepAliveTime is now wired to a real TCP keep-alive socket option (via SocketsHttpHandler.ConnectCallback) rather than the inert HTTP/2 ping timeout, which had no effect on HTTP/1.1. It enables SO_KEEPALIVE and sets the per-socket idle time on Windows, Linux, and macOS; on other platforms keep-alive stays enabled at the OS default idle time.
• Compression is now a {None, Deflate} enum defaulting to Deflate (compression on by default); the driver sends Accept-Encoding: deflate by default. Set Compression.None to disable. The deprecated EnableCompression bool is preserved only as a compatibility shim mapping true/false to Compression.Deflate/Compression.None.

New options

• Ssl (SslClientAuthenticationOptions) - adds client-certificate and custom-CA support. SkipCertificateValidation is applied to an internal copy rather than mutating the caller's options.
• DefaultBatchSize (64) - connection-level default that fills the per-request batchSize when unset.
• MaxResponseHeaderBytes - the maximum response header size, in bytes (converted internally to the handler's native kilobyte unit).
• ReadTimeout - a per-read idle timeout applied to each read of the response stream (via per-read CancelAfter).
• Proxy (IWebProxy) - routes connections through an HTTP proxy.
• GremlinServer.FromUrl(string) / GremlinServer(Uri) - configure the endpoint from a single URL (scheme, host, port, path), deriving SSL from the scheme. The existing host/port/path constructor remains.

Removed (breaking)

• maxResponseContentLength - responses now stream; ReadTimeout is the partial mitigation.

Bug fixes

• Fixed deflate response decompression, which threw on the server's zlib-framed output because it used DeflateStream (raw DEFLATE, RFC 1951) instead of ZLibStream (zlib, RFC 1950). The bug was previously masked because compression was off by default; turning it on by default would have made it a default-path failure.
• Fixed Ssl options cloning (used on the skip-certificate-validation path) to copy ClientCertificateContext and AllowTlsResume, which were previously dropped, breaking mTLS client certificates and silently re-enabling TLS resumption.

Testing

• gremlin-dotnet unit tests pass (695 tests), including new ConnectionSettingsTests and the ReadTimeout slow-read timeout test.
• CHANGELOG, reference config table (gremlin-variants.asciidoc), and upgrade guide (release-4.x.x.asciidoc) updated for the .NET slice.

Assisted-by: Kiro: Claude Opus 4.8

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.83%. Comparing base (a28cd1f) to head (fe0a256).
⚠️ Report is 144 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3468      +/-   ##
============================================
- Coverage     76.35%   75.83%   -0.53%     
- Complexity    13424    13650     +226     
============================================
  Files          1012      995      -17     
  Lines         60341    55471    -4870     
  Branches       7075     7209     +134     
============================================
- Hits          46076    42067    -4009     
+ Misses        11548    10822     -726     
+ Partials       2717     2582     -135     

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[kenhuuu]

VOTE +1