Storing system descriptor

[sdjukicTT]

Ticket

#201

Problem description

Default system descriptor used in TTIRToTTNNBackendPipeline can't be used for multichip, actual current system descriptor is needed.

What's changed

We store the system descriptor and then set options.systemDescPath.

Checklist

• New/Existing tests provide coverage for changes

[github-actions]

	Tests	Passed ✅	Skipped ⚠️	Failed
TT-XLA Tests	603 ran	432 passed	171 skipped	0 failed

Test	Result
No test annotations available

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.57%. Comparing base (0a01029) to head (0643634).
Report is 32 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/common/module_builder.cc	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #265      +/-   ##
==========================================
+ Coverage   78.06%   78.57%   +0.50%     
==========================================
  Files          21       21              
  Lines        1044     1008      -36     
==========================================
- Hits          815      792      -23     
+ Misses        229      216      -13     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mrakitaTT]

Input-only arguments should be ordered before the output or in-out arguments, see more here: https://google.github.io/styleguide/cppguide.html#Inputs_and_Outputs

[mrakitaTT]

Check after this if std::filesystem::exists(cached_system_descriptor_path_) and if it doesn't, do:

DLOG_F(ERROR, "Failed to store the system descriptor to the disk using path: %s",
    cached_system_descriptor_path_.c_str());
return tt_pjrt_status::kInternal;

[mrakitaTT]

Please add a TODO comment here explaining that this name would need to be unique to avoid clashes between multiple clients, but since we plan soon to remove the need for storing the descriptor to the disk we are leaving it simple like this until then (or until it causes problems).