feat(guest): publish Reth stateless validator ELFs

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Closes #35.

Upstreams the canonical Reth stateless validator guest and execution-spec SSZ contract into paradigmxyz/stateless. The guest consumes statelessInputBytes unchanged, validates through Reth with the Zeth sparse trie, and emits statelessOutputBytes.

Adds locked entrypoints for OpenVM v2.0.0, SP1 v6.3.1, and ZisK v1.0.0-alpha, plus public CI that builds, key-generates, checksums, attests, and publishes the final .elf and .vk assets from v* tags. The shared zkvm-interface Crypto/CryptoProvider implementation now lives in stateless, while the regular host API continues to use Reth's sparse trie by default.

Validation

• tests-zkevm@v0.6.2: completed with the same 17 known Reth divergences tracked by the current ere-guests integration.
• Independent and GitHub Actions compiler-image builds plus verification-key generation completed for all three zkVMs; every .elf and .vk was byte-for-byte identical across the two machines.
• A 5,822-byte Amsterdam fixture executed successfully in all three final ELFs and produced the expected canonical statelessOutputBytes.
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --exclude ef-tests --exclude stateless-validator-tests
• All five no_std configurations in scripts/check_no_std.sh
• Full local default-trie EF suite: 62/62 passed in 5,081.976 seconds. GitHub's EF matrix also passed with both the default trie (22m16s) and Zeth trie (22m03s).

zkVM	ELF size	ELF SHA-256
OpenVM v2.0.0	3,584,988 bytes	e2049a17c751a4c91fe979985864fa38805541917d1f855d57d2b00566413409
SP1 v6.3.1	3,801,888 bytes	0f274cff9d0c4676f9c28d11e151f4351dce4cb5caf89223884494e715f93fe3
ZisK v1.0.0-alpha	3,746,280 bytes	42732b93fe877743089d2734c2a3a35e5029616f4c234db2a388d20505902e31