starknet_transaction_prover: add manual testing guide

[avi-starkware]

Adds the manual testing guide for the prover service (split out of #14052 to keep that PR focused on the deployment smoke script + its guide, which reference this document).

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[cursor]

PR Summary

Low Risk
Documentation-only change; no application code or runtime behavior is modified.

Overview
Adds MANUAL_TESTING_GUIDE.md under crates/starknet_transaction_prover as the full deep-validation playbook for deployed proving services, with DEPLOYMENT_SMOKE_TESTING_GUIDE.md called out for shorter post-deploy checks.

The guide walks engineers through copy-paste curl/jq/shell flows: prerequisites and config (K8s ConfigMap vs local cargo run), rpc_call / find_tx_hash helpers, happy-path starknet_specVersion and starknet_proveTransaction (INVOKE v3 from chain RPC), and negative cases with expected JSON-RPC codes. It also covers CORS, compression, concurrency (-32005), load (vegeta/hey), optional TLS, OHTTP, body size limits, env-var config, observability, a section 15 checklist, and a results template for audit trails.

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[avi-starkware]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• starknet_transaction_prover: add deployment smoke script and guide #14052
• starknet_transaction_prover: add manual testing guide #14404 👈 (View in Graphite)
• starknet_transaction_prover: make RPC error spec test exhaustive via enum #14051
• 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
• starknet_transaction_prover: add request body size limit tests #14403
• main-v0.14.3

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[reviewable-StarkWare]

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