- r402-svm: make `serde_json` and `tokio` optional; gate behind client/server/facilitator features; remove unused `solana-keypair` dev-dependency
- r402-evm: make `alloy-sol-types` optional; gate behind client and facilitator features
- r402-http: make `r402`, `serde_json`, and `thiserror` optional; gate behind client/server/telemetry features; add `use-as-underscore` for `tokio` and `wiremock` dev-dependencies

Resolves `unused-crate-dependencies` errors when `-D warnings` is enabled.