RUBY-3700 Do not clear pool on retryable errors

[comandeo-mongo]

This PR is a part of the client backpressure initiative. Here we make sure that a connection pool is not cleared if a retryable error (in terms of the client backpressure spec) happens.

[Copilot]

Pull request overview

This PR updates connection-establishment error handling to support the client backpressure initiative by preventing SDAM state changes / pool clearing for retryable (backpressure-signaled) handshake network errors.

Changes:

• Add SystemOverloadedError (and RetryableError) labeling to handshake network errors during connection establishment.
• Skip marking the server Unknown (and thus skip pool clearing) when a handshake SocketError/SocketTimeoutError is labeled SystemOverloadedError.
• Add unified SDAM backpressure spec tests and adjust an existing CMAP spec test to use a command error instead of a forced connection close.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lib/mongo/server/pending_connection.rb	Adds error labeling during handshake failures to support backpressure behavior.
lib/mongo/server/connection_pool.rb	Changes connection creation error handling to avoid unknown! (pool clear) for SystemOverloadedError-labeled handshake failures and to order events correctly.
lib/mongo/server.rb	Updates handshake failure handling to avoid unknown! when SystemOverloadedError is present.
spec/mongo/server/connection_spec.rb	Removes an expectation that handshake network errors mark the server unknown.
spec/spec_tests/data/cmap/pool-create-min-size-error.yml	Adjusts CMAP spec to use a command error (errorCode) for minPoolSize population error.
spec/spec_tests/data/sdam_unified/backpressure-server-description-unchanged-on-min-pool-size-population-error.yml	Adds unified SDAM test asserting server description doesn’t change on minPoolSize handshake backpressure error.
spec/spec_tests/data/sdam_unified/backpressure-network-timeout-fail-single.yml	Adds unified SDAM test asserting no pool clear + expected labels on handshake timeout backpressure.
spec/spec_tests/data/sdam_unified/backpressure-network-timeout-fail-replicaset.yml	Same as above for replicaset topology.
spec/spec_tests/data/sdam_unified/backpressure-network-error-fail-single.yml	Adds unified SDAM test asserting no pool clear + expected labels on handshake network error backpressure.
spec/spec_tests/data/sdam_unified/backpressure-network-error-fail-replicaset.yml	Same as above for replicaset topology.

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