Accept JSON-RPC requests without a params field

[tomaka]

Fix #3080

[mergify]

Automatically approving tomaka's pull requests. This auto-approval will be removed once more maintainers are active.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

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 Delta Bytes │ Item
─────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
      +46825 ┊ smoldot::json_rpc::methods::MethodCall::from_defs::h51e05694fc74eea8
      -42137 ┊ smoldot::json_rpc::methods::MethodCall::from_defs::h7d11981beb5d80d8
        +152 ┊ <serde_json::ser::Compound<W,F> as serde::ser::SerializeStruct>::serialize_field::hcd7c0ce45da9b2c7
         -79 ┊ smoldot::json_rpc::parse::_::<impl serde::ser::Serialize for smoldot::json_rpc::parse::SerdeCall>::serialize::h1e4878f39c6734c6
         +60 ┊ smoldot::json_rpc::parse::build_call::hc73ae00d5571c2d9
         -51 ┊ <serde_json::de::MapAccess<R> as serde::de::MapAccess>::next_value_seed::h755a5dac75dd24f4
         +34 ┊ smoldot::json_rpc::parse::parse_call::hf04df0813880bd39
         +26 ┊ core::ptr::drop_in_place<core::option::Option<core::result::Result<alloc::vec::Vec<&serde_json::raw::RawValue>,serde_json::error::Error>>>::h7faf34a76144760f
         -13 ┊ <&mut serde_json::de::Deserializer<R> as serde::de::Deserializer>::deserialize_struct::h9a08479ee9894006
       +5024 ┊ Σ [9 Total Rows]