chore: add mock system mode enum

[nadin-Starkware]

Stack:

• feat: add test case for remote connection flow #2587
• chore: add mock_system_mode to the create config function #2585
• chore: return vector of SequencerNodeConfig in create config function #2584
• chore: add get_http_server_config function #2583
• chore: change sequencer_node_handle type to Vec to support multiple handles #2572
• chore: add serial_test crate #2555
• chore: add mock system mode enum #2554 ⬅
• chore: configure tracing only once #2553

⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.

[reviewable-StarkWare]

This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.09%. Comparing base (64649bd) to head (f2a3e90).

Additional details and impacted files

@@                  Coverage Diff                  @@
##           spr/main/d56e92a1    #2554      +/-   ##
=====================================================
- Coverage              38.68%   34.09%   -4.60%     
=====================================================
  Files                    278      276       -2     
  Lines                  32136    32105      -31     
  Branches               32136    32105      -31     
=====================================================
- Hits                   12432    10946    -1486     
- Misses                 18665    20165    +1500     
+ Partials                1039      994      -45     

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