fix(test): timeout in rpc_regression_tests

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

• download test snapshots in parallel

Reference issue to close (if applicable)

Closes #5146

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[LesnyRumcajs]

@hanabi1224 I wonder if we could avoid handling this ourselves. Nextest runs tests in parallel, so if we split the tests into smaller ones, e.g., one test per endpoint type, we could get it for free. I imagine this could be done with a limited amount of macros.

Would it be feasible?

[hanabi1224]

@LesnyRumcajs I feel data-driven testing framework in Rust is not yet super mature, https://crates.io/crates/datatest requires nightly features and https://crates.io/crates/datatest-stable requires complicated configurations. How about merging this to unblock CI and tackle data-driven testing later?