Persist EVM setup keys before verifier generation

[peter941221]

Summary

Persist reusable EVM setup artifacts before attempting Solidity verifier generation.

Problem

cargo openvm setup --evm generates the aggregation/Halo2 key material before calling generate_halo2_verifier_solidity(), but it only writes those reusable artifacts to disk afterwards.

If verifier generation fails, the command exits before persisting:

• agg_stark.pk
• agg_stark.vk
• agg_halo2.pk
• root.asm

This forces the next run to regenerate expensive key material unnecessarily.

Change

Write the reusable setup artifacts before Solidity verifier generation in the EVM setup path:

• write agg_stark.pk
• write agg_stark.vk
• write agg_halo2.pk
• write root.asm
• then call generate_halo2_verifier_solidity()
• then write the verifier contract bundle

This keeps the fix scoped to CLI-side ordering without changing SDK key generation or verifier generation behavior.

Verification

• cargo +nightly fmt --all -- --check
• git diff --check

Local cargo check remains blocked on this Windows machine by an MSVC/libgit2 link environment issue unrelated to setup.rs.

Closes #2356.