Fix PySCF startup timeout

[fallintoplace]

Summary

• Require PySCF health checks to return status: available before the driver reports ready.
• Keep startup polling through REST connection failures until the timeout expires.
• Drop unused local variables in the startup path.

Why

When RestClient::get() throws while the PySCF server is still starting or unreachable, the previous loop continued before incrementing or checking the timeout counter. That could hang forever on connection failures. The availability checks also treated malformed or non-ready responses as available.

Validation

• git diff --check

Not run locally: full solvers build, because this checkout does not have a configured CUDA-Q/LLVM build environment.

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