Split test library

[Odonno]

Is your feature request related to a problem? Please describe.

Related to #58, testing can be tedious and there is some critical paths about tests:

• tests should run fast (less than 10s), so they should run in parallel
• tests on "branches" feature cannot be run in parallel because they use the same namespace/database in a SurrealDB instance

Describe the solution you'd like

If possible, split test library into 2 or 3:

• one for "standard" tests
• one for "e2e" tests (longer test, with waiting time)
• one for each limited scope tests, so one for "branches" tests

Describe alternatives you've considered

Use flags with cargo-nextest. Need first to migrate to this tool. #59

Additional context

N/A