feat(test-tools): Add run_tasks fixture

[khvn26]

This PR is a PoC for the run_tasks fixture.

By default, we run tasks synchronously in tests. However, in order to test complex workflows that require asynchronous processing, we need a way to schedule and run tasks as they would've been run with TASK_PROCESSOR_MODE enabled. The new fixture makes sure TASK_RUN_METHOD is set to TASK_PROCESSOR in the context of a test using it, and allows to run a pre-determined number of tasks to verify their operation.

Usage:

def test_logic_involving_async_processing(run_tasks: RunTasksFixture) -> None:
   # When
   # code scheduling a task is called
   my_logic()

   # Then
   task_runs = run_tasks(num_tasks=1)

   # The task was failed
   assert task_runs[0].result == "FAILURE"

We can probably pack the assertion logic in a fixture as well to allow something like an AssertTaskRunFixture:

def test_logic_involving_async_processing(assert_task_run: AssertTaskRunFixture) -> None:
   # When
   my_logic()

   # Then
   assert_task_run("my_module.my_task", "FAILURE")

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 74.41860% with 11 lines in your changes missing coverage. Please review.

Project coverage is 94.08%. Comparing base (abec78b) to head (aea8a76).

Files with missing lines	Patch %	Lines
src/common/test_tools/plugin.py	50.00%	8 Missing ⚠️
src/common/test_tools/types.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #85      +/-   ##
==========================================
- Coverage   94.42%   94.08%   -0.35%     
==========================================
  Files          74       73       -1     
  Lines        2208     2232      +24     
==========================================
+ Hits         2085     2100      +15     
- Misses        123      132       +9     

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