fix(prover-nitro-enclave): use Linux-only deps for real main

[DoddHazlittlrduq]

issue:

The binary's async main, eyre return type, and NitroEnclave import are #[cfg(target_os = "linux")]; non-Linux builds only compile a panic stub.

Put eyre, base-proof-tee-nitro-enclave, and tokio under [target.'cfg(target_os = "linux")'.dependencies] so cargo-udeps does not flag them on other hosts.

Summary

Scope base-prover-nitro-enclave runtime dependencies to Linux only, matching main.rs cfg split.

Motivation

On non-Linux targets, only the panic!(...) stub main is compiled; tokio, eyre, and base-proof-tee-nitro-enclave are unused in depinfo. Unconditional [dependencies] causes cargo udeps false positives on macOS and similar CI matrices.

Changes

• bin/prover/nitro-enclave/Cargo.toml: replace top-level [dependencies] with [target.'cfg(target_os = "linux")'.dependencies] for eyre, base-proof-tee-nitro-enclave, and tokio (waterfall-sorted).

Verification

• cargo check -p base-prover-nitro-enclave
• RISC0_SKIP_BUILD_KERNELS=1 cargo +nightly udeps --locked -p base-prover-nitro-enclave --all-features --all-targets

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