refactor(plugins): move SSL classifiers into PluginKit and drop the test mirror

[datlechin]

Problem

Each plugin's classifySSLError (maps a driver's raw TLS error string to an SSLHandshakeError) was duplicated by hand in TableProTests/PluginTestSources/PluginSSLClassifiers.swift, because registry-only plugin code is not compiled into the TableProTests target. The real function and its mirror had to be kept byte-identical or the tests would pass while the shipped logic differed. The mirror had already drifted (FreeTDS returned a different type in the mirror than in the plugin, and Cassandra's real classifier was not mirrored at all).

This applies the same pattern as #1740 (OracleChannelFatalCode) to all eight plugin SSL/TLS classifiers.

Change

Extracted the pure classification logic into shared public types and pointed each plugin at it:

• TableProPluginKit (one type per plugin): LibPQSSLClassifier, MariaDBSSLClassifier (holds sslOnlyErrorCodes + classifySSLError(code:message:)), MongoDBSSLClassifier, RedisSSLClassifier, OracleSSLClassifier, ClickHouseSSLClassifier, CassandraClientKeyClassifier. Tested in PluginSSLClassifierTests via import TableProPluginKit.
• TableProMSSQLCore: MSSQLTLSClassifier. MSSQL's classifier returns MSSQLTLSFailureKind (which lives in that module, not in PluginKit), so it lives with the enum and is tested by the package's own TableProMSSQLCoreTests.
• Cassandra's classifySSLError(rc:message:) stays in the plugin (it depends on the C CassError type); only its pure client-key logic moved.

Deleted the 191-line mirror PluginSSLClassifiers.swift and retargeted the tests at the real public types. Logic moved verbatim, so behavior is unchanged.

Adding new public types to PluginKit is additive ABI: no currentPluginKitVersion bump.

Verification

• App target and all plugin targets: BUILD SUCCEEDED, 0 errors.
• PluginSSLClassifierTests (7 plugin suites): all pass.
• TableProMSSQLCoreTests MSSQL TLS suite: 6/6 pass.