Parallel Electrum integration tests can fail installing rustls CryptoProvider

[reez]

Running the network-gated integration suite with default test concurrency can fail when parallel Electrum clients initialize rustls at the same time... rerunning the failed Electrum canary alone passed, and dart test test/integration --concurrency=1 passed.

CouldNotCreateConnectionElectrumException(unexpected error: Failed to install CryptoProvider)
package:bdk_dart/bdk.dart 26094:5                        checkCallStatus
package:bdk_dart/bdk.dart 26117:5                        rustCall
package:bdk_dart/bdk.dart 21731:15                       new ElectrumClient
test/integration/integration_helpers.dart 55:10          buildElectrumClientFromEnv
test/integration/wallet_surface_canary_test.dart 153:26  main.<fn>.<fn>

[j-kon]

Thanks for opening this, @reez.

This looks like a test concurrency issue around Electrum/rustls initialization rather than a wallet behavior failure, especially since the failed canary passed when rerun alone and dart test test/integration --concurrency=1 passed.

I'm interested in helping with this. I can take a look at the integration test setup and see whether we should document/run the network-gated Electrum suite serially, or add a focused test runner/config change so the Electrum canaries don't initialize in parallel.

I'll avoid mixing this with PR #94 since that PR is offline SQLite lifecycle coverage.