fix(genvm): serve latest-finalized storage reads from finalized state 🐛

[kp2pml30]

Fixes #1791

Problem and outcome

A cross-contract view(state=LATEST_FINAL) / LATEST_FINALIZED makes GenVM call host storage_read with mode 1. Host.storage_read had assert type != StorageView.LATEST_FINALIZED; the AssertionError escaped the host loop, and run_genvm_host treated it as a transient failure, retrying with exponential backoff (5s, 10s, 20s, …) until the 600s budget ran out:

• gen_call hangs for 600s and returns -32603 Internal error (behind Cloudflare: 524 after ~125s)
• writes end with CONSENSUS_LEADER_EXEC_TIMEOUT / Leader execution exceeded 600.000s

The prd image (v0.121.24) and v0.123-dev both contain the assert.

Now LATEST_FINALIZED reads are served from the contract's finalized state. Slots without a finalized value (including contracts that are not finalized yet, or have no finalized bucket) read as zeroes. DEFAULT / LATEST_DECIDED reads are unchanged.

Implementation and validation

• StateProxy.storage_read_finalized: defaults to zeroes, for proxies with no finalized state such as _StateProxyNone
• _SnapshotView implements it over states["finalized"]. The decode caches are now keyed by state status, so accepted and finalized reads of the same slot can't alias, and writes don't leak into the finalized view
• tests/unit/test_storage_read_latest_finalized.py: red on v0.123-dev (the AssertionError), green with the fix. Full tests/unit/ suite passes

Local stack, with a minimal source and caller contract (not the reporter's code):

Build	Call	Result
v0.121.24 (prd)	read_default, read_latest_non_final	OK, 1.0s
v0.121.24 (prd)	read_latest_final	-32603 after 600.2s; 7 GenVM attempts, each AssertionError in host_loop
this PR	read_latest_final	OK, 0.3s
this PR	set_marker accepted, not finalized	non-final returns the new value, finalized returns the old value
this PR	after finalization	both views return the new value
this PR	consume_latest_final write	MAJORITY_AGREE, leader SUCCESS, 15s

Not in scope

• Retry policy: any non-HostException raised from a host callback still turns into retries until the time budget runs out
• LATEST_DECIDED: still follows the run's state_status, which read_contract_major relies on

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