Fix middleware functions with implicit, return type-only generic parameters

[MajorLift]

Motivation

• Middleware functions in eth-json-rpc-middleware, eth-json-rpc-engine, eth-json-rpc-infura are "return type-only" generics with implicit generic parameters. This is a discouraged pattern.
• Redefining the functions to expose the generic parameters that are implicitly hard-coded into their return type would make them less brittle to future typing updates.
  • Example error: "JsonRpcMiddleware<unknown, unknown> is not assignable to parameter of type JsonRpcMiddleware<JsonRpcParams, Json>"

// before
function createExampleMiddleware(exampleParam): JsonRpcMiddleware<JsonRpcParams, Json>
// after
function createExampleMiddleware<
  Params extends JsonRpcParams = JsonRpcParmas, 
  Result extends Json = Json
>(exampleParam): JsonRpcMiddleware<Params, Result>

Tasks

• Compile list of functions and types to be fixed.
• Expose the return type generic params in the outer type/function.
  • Assign default arguments to provide a consistent interface and minimize disruption.
• Add contributor-docs TypeScript style-guide entry
  • Initial notes added here: Complete TypeScript guidelines contributor-docs#69 (comment)
• Look into adding eslint rules for avoiding return type-only generics.