fix(prover-nitro-enclave): use Linux-only deps for real main (base#1757)

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.

Author: DoddHazlittlrduq

bin/prover/nitro-enclave/Cargo.toml

@@ -15,7 +15,7 @@ path = "src/main.rs"
 [lints]
 workspace = true
 
-[dependencies]
+[target.'cfg(target_os = "linux")'.dependencies]
 eyre.workspace = true
 base-proof-tee-nitro-enclave.workspace = true
 tokio = { workspace = true, features = ["macros", "rt-multi-thread"] }