starknet_os_flow_tests: build OS initial reads via get_os_initial_reads

[yoavGrs]

Enable blockifier/os_input for the flow tests and replace the local get_extended_initial_reads helper with CachedState::get_os_initial_reads, so the tests build the OS initial reads exactly as production does.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

This change is 

[yoavGrs]

• blockifier,apollo_batcher: trim OS initial reads to the accessed-key set #14595
• starknet_os_flow_tests: build OS initial reads via get_os_initial_reads #14594 👈 (View in Graphite)
• apollo_consensus_orchestrator: forward OS initial reads into the cende blob #14593
• blockifier,apollo_batcher: produce OS initial reads behind os_input #14592
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[cursor]

PR Summary

Low Risk
Test-only refactor in integration tests; behavior should match production more closely via the shared blockifier API.

Overview
Starknet OS flow tests now build block initial reads the same way the batcher/executor does, instead of a crate-local helper.

The blockifier dev-dependency gains the os_input feature so tests can call CachedState::get_os_initial_reads. In test_manager, both places that fed OsBlockInput / decompression (per-block build and full-run TestRunner::run) switch from get_extended_initial_reads to that API. The duplicated get_extended_initial_reads implementation is removed from utils.rs (and the unused StateMaps import there).

This keeps integration tests aligned with production OS initial-read construction (including write-only access back-fill in blockifier), with no production code changes.

^{Reviewed by Cursor Bugbot for commit d493b74. Bugbot is set up for automated code reviews on this repo. Configure here.}

[itamar-starkware]

@itamar-starkware reviewed 3 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on yoavGrs).