chore: correct the types of Rpc{Batch}Request to prevent type errors in Connection.ts

[steveluscher]

Problem

The return value of these was incorrect, leading to an any propagating through the code, which led to real breakages in the framework (eg. #26099).

Summary of Changes

When we properly represent this return type as a promise for an array then array methods like map() return correct types.

[codecov]

Codecov Report

Merging #26102 (2ef5933) into master (aea84e6) will not change coverage.
The diff coverage is n/a.

❗ Current head 2ef5933 differs from pull request most recent head 1478e4a. Consider uploading reports for the commit 1478e4a to get more accurate results

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  Misses        450      450           
  Partials      119      119