chore: bootstrapping task-manager through feature flags

[gruberb]

Description

This PR introduces the TaskManager to the codebase. It is an in-between step, whereas we can benchmark two different implementations of the TaskManager

• task-manager-futures: Using FuturesUnordered for tasks to remove themselves after being done.
• task-manager-channel: To send a message to the TaskManager and removing them by hand.

Fixes TP-644

Additions and Changes

Feature flag task-manager-channels to build and run the codebase with the channels implementation instead of the futures one.

task-manager-futures runs by default and gets deactivated when using the features flag task-manager-channels.

New feature (non-breaking change which adds functionality)

Splitting the work of the double_echo into tasks, and let them run in parallel.

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works

[codecov]

Codecov Report

Merging #266 (55b0530) into main (0fa742a) will decrease coverage by 0.44%.
The diff coverage is 89.93%.

@@            Coverage Diff             @@
##             main     #266      +/-   ##
==========================================
- Coverage   52.99%   52.56%   -0.44%     
==========================================
  Files         207      203       -4     
  Lines        9978     9803     -175     
==========================================
- Hits         5288     5153     -135     
+ Misses       4690     4650      -40     

Files Changed	Coverage Δ
crates/topos-tce-broadcast/src/constant.rs	40.00% <0.00%> (-26.67%)	⬇️
...s-tce-broadcast/src/double_echo/broadcast_state.rs	83.91% <50.00%> (-1.20%)	⬇️
...pos-tce-broadcast/src/task_manager_futures/task.rs	90.90% <71.42%> (-2.43%)	⬇️
...opos-tce-broadcast/src/task_manager_futures/mod.rs	85.00% <87.50%> (-2.50%)	⬇️
crates/topos-tce-broadcast/src/lib.rs	89.13% <90.00%> (+0.49%)	⬆️
crates/topos-tce-broadcast/src/double_echo/mod.rs	82.43% <97.14%> (+18.43%)	⬆️
crates/topos-tce-broadcast/src/tests/mod.rs	100.00% <100.00%> (+2.15%)	⬆️

... and 6 files with indirect coverage changes