Fixed database and improved resilience of CAPIO

[marcoSanti]

This pull request significantly improves the resilience of CAPIO. in particular:

• Reverted check around lock guard, as it was introducing bugs
• Wrapped syscall handler invocations with try/catch blocks to print also in release mode the error should it arise
• Wrapped FSMonitor class with try/catch blocks to ensure error print to be correct
• Fixed an issue with the termination of capio: now if the signal handler is invoked by a child thread, it is skipped, so that only the main thread cleans the allocated data structures
• Fixed a database on handshake: now the server-to-client and client-to-server she queues are allocated before sending a handshake to the server, ensuring that the server does not fail when issuing a stat on the shm allocated element. (it previously returned size 0 on the stat, thus failing on the mmap)
• Added a single retry when getting the sim element size trough stat()

[codecov]

Codecov Report

Attention: Patch coverage is 17.15976% with 140 lines in your changes missing coverage. Please review.

Project coverage is 47.49%. Comparing base (d1f45fc) to head (6661c98).
Report is 1 commits behind head on capio-v2.

Files with missing lines	Patch %	Lines
src/server/file-manager/fs_monitor.hpp	10.81%	12 Missing and 21 partials ⚠️
...c/server/client-manager/request_handler_engine.hpp	4.54%	4 Missing and 17 partials ⚠️
src/common/capio/shm.hpp	32.14%	8 Missing and 11 partials ⚠️
src/posix/libcapio_posix.cpp	5.26%	4 Missing and 14 partials ⚠️
src/server/communication-service/MTCL_backend.hpp	0.00%	6 Missing and 7 partials ⚠️
src/server/capio_server.cpp	25.00%	0 Missing and 9 partials ⚠️
src/posix/utils/cache.hpp	0.00%	0 Missing and 7 partials ⚠️
src/server/utils/signals.hpp	0.00%	1 Missing and 5 partials ⚠️
src/server/file-manager/file_manager_impl.hpp	44.44%	1 Missing and 4 partials ⚠️
src/common/capio/env.hpp	0.00%	0 Missing and 1 partial ⚠️
... and 8 more

Additional details and impacted files

@@             Coverage Diff              @@
##           capio-v2     #144      +/-   ##
============================================
- Coverage     48.79%   47.49%   -1.31%     
============================================
  Files            74       73       -1     
  Lines          3947     4009      +62     
  Branches       2270     2345      +75     
============================================
- Hits           1926     1904      -22     
+ Misses          980      936      -44     
- Partials       1041     1169     +128     

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