feat(stateless): add zkVM crypto provider

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Summary

Adds the standard zkVM-backed revm Crypto and Alloy CryptoProvider implementation currently maintained in ere-guests to stateless behind an optional zkvm-interface feature.

The feature is disabled by default and preserves the existing ERE implementation. SP1-specific caches and MODEXP fast paths are intentionally out of scope for this ownership change.

Consumer proof

Replaced the duplicate provider in an ERE v0.13.0 worktree and compiled both complete Reth guest workspaces:

• stateless-validator-reth-sp1
• stateless-validator-reth-zisk

Checks

• cargo fmt --all --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace
• cargo test -p stateless --features zkvm-interface --lib --no-run
• ./scripts/check_no_std.sh
• RISC-V no_std build with --features zkvm-interface
• stateless docs with warnings denied