Added Capio Discovery Service

[marcoSanti]

Added CAPIO Discovery Service

This PR introduces the CAPIO Discovery Service, enabling CAPIO server instances to detect and communicate with other running server instances in the cluster.

Changes

• Added a new filesystem-based and multicast-based discovery service (discovery_service.cpp) that allows server instances to register themselves and detect peers
• Began adding support in the capio backend for explicit connection, by introducing the virtual method connect_to
• Migrated management of the CAPIO canary flag into the discovery service, centralising server lifecycle logic
• Updated CLI parsing logic to correctly handle the startup sequence with the new discovery service in place
• Refactored the shared memory canary (shm_canary.cpp) to work alongside the new service

[codecov]

Codecov Report

❌ Patch coverage is 27.56410% with 113 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.42%. Comparing base (4e0e932) to head (9c05b23).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
capio/server/src/discovery_service.cpp	10.58%	49 Missing and 27 partials ⚠️
capio/server/capio_server.cpp	63.15%	5 Missing and 9 partials ⚠️
capio/server/src/shm_canary.cpp	25.00%	6 Missing and 6 partials ⚠️
capio/server/include/remote/listener.hpp	37.50%	1 Missing and 4 partials ⚠️
capio/server/include/utils/signals.hpp	42.85%	1 Missing and 3 partials ⚠️
capio/server/src/mpi_backend.cpp	0.00%	1 Missing ⚠️
capio/server/src/none_backend.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #233      +/-   ##
==========================================
- Coverage   63.84%   62.42%   -1.43%     
==========================================
  Files          77       79       +2     
  Lines        3214     3300      +86     
  Branches     1997     2042      +45     
==========================================
+ Hits         2052     2060       +8     
- Misses        381      432      +51     
- Partials      781      808      +27     

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