starknet_transaction_prover: make RPC error spec test exhaustive via enum

[avi-starkware]

Replaces the ad-hoc test_cases vec in test_error_responses_match_spec
with a KnownRpcError test-only enum whose spec_key and
sample_error_object matches are exhaustive — adding a new variant
forces both matches to be updated, and the bidirectional set-equality
check between KnownRpcError::ALL and the spec's components/errors
keys guarantees the enum and the OpenRPC spec stay in sync.

Drops the pre-existing 'TODO(Avi): Add an error enum to make this
test exhaustive' tag.

[reviewable-StarkWare]

This change is 

[avi-starkware]

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• starknet_transaction_prover: add deployment health docs and smoke script #14052
• starknet_transaction_prover: make RPC error spec test exhaustive via enum #14051 👈 (View in Graphite)
• starknet_transaction_prover: add TLS integration tests #14050
• starknet_transaction_prover: add ServiceConfig validation tests #14049
• starknet_transaction_prover: add CORS validation unit tests #14048
• starknet_transaction_prover: add prover input validation unit tests #14047
• starknet_transaction_prover: add committer utils unit tests #14046
• main-v0.14.3

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[cursor]

PR Summary

Low Risk
Test-only refactor in rpc_spec_test.rs; no production RPC or error handling behavior changes.

Overview
Refactors test_error_responses_match_spec so OpenRPC error coverage is driven by a test-only KnownRpcError enum instead of a hand-maintained test_cases vector.

Each variant maps to a spec key via spec_key() and to a sample ErrorObjectOwned via sample_error_object(); exhaustive matches mean adding a new RPC error requires updating those methods and listing the variant in KnownRpcError::ALL. The test still checks each sample against SpecError::from_spec, and now also enforces bidirectional sync between KnownRpcError keys and SPEC_ERRORS (with a guard against duplicate keys in ALL). The old TODO about making the test exhaustive is removed.

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