Inject LambdaVM crypto into the ethrex guest

[jotabulacios]

This PR builds on #666 by adding ECSM-accelerated secp256k1_ecrecover and moving the crypto implementation into this repo.

Accelerates secp256k1_ecrecover via the ECSM precompile. The ECDSA recovery's linear combination pk = u1·G + u2·R is evaluated through four x-only ecsm_mul queries and full-point reconstruction via the chord law, with all three inversions batched. Falls back to pure-Rust ProjectivePoint::lincomb for degenerate cases (zero scalars, identity points, cancelling terms). Uses the existing x-only ABI — no executor or prover changes required. keccak256 continues routing to the keccak_permute precompile as before.

Moves the crypto implementation into this repo as a new crate crypto/ethrex-crypto (lambda-vm-ethrex-crypto). Previously the LambdaVmCrypto impl lived inside the ethrex repo (crates/guest-program/src/crypto/lambdavm.rs). The guest now constructs LambdaVmEcsmCrypto from this crate and injects it via Arc<dyn Crypto> — crypto changes no longer require an ethrex PR.

Validation

• crypto/ethrex-crypto host tests: 5/5 — lincomb2 correctness on fixed inputs and recovery shape, plus three degenerate fallback guards (edge scalars, identity points, cancelling terms).
• Guest ELF builds for riscv64, links clean.
• Cycle counts on vm-benchmarks-1 — each ETH transfer triggers one secp256k1_ecrecover:

Block	ecrecover	Cycles
simple_tx (1 tx)	software k256	4,642,452
simple_tx (1 tx)	ECSM (this PR)	1,794,386
10 transfers	ECSM (this PR)	6,879,038