fix: address review feedback on module docs

- Gate dashmap import behind cfg(feature=std) (fixes no_std build)
- Update cache docs to reference ArtifactId instead of raw tuple
- Fix interop-tests docs to list actual backends (ring + RustCrypto)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: EffortlessSteven

crates/uselesskey-core-cache/src/lib.rs

@@ -3,7 +3,7 @@
 //! Identity-keyed typed cache primitives for uselesskey fixture factories.
 //!
 //! Provides a concurrent, identity-based cache that stores generated cryptographic
-//! artifacts keyed by `(domain, label, spec, variant)` tuples. This avoids
+//! artifacts keyed by [`ArtifactId`](uselesskey_core_id::ArtifactId). This avoids
 //! expensive re-generation (especially RSA) across test runs.
 
 extern crate alloc;
@@ -13,6 +13,7 @@ use alloc::collections::BTreeMap;
 use alloc::sync::Arc;
 use core::any::Any;
 use core::fmt;
+#[cfg(feature = "std")]
 use dashmap::DashMap;
 #[cfg(not(feature = "std"))]
 use spin::Mutex;

crates/uselesskey-interop-tests/src/lib.rs

@@ -1,5 +1,5 @@
 //! Cross-backend interoperability tests for uselesskey.
 //!
 //! Verifies that keys generated by uselesskey work correctly across multiple
-//! cryptographic backends (ring, aws-lc-rs, rustls, RustCrypto, jsonwebtoken).
+//! cryptographic backends (ring and RustCrypto crates such as p256, ed25519-dalek, rsa).
 // Cross-backend interoperability tests — see tests/ directory.