Do not crash on torch.export

[gilfree]

Fix file name length issue when torch.export.export is called under depyf

The name used in the lazy_format_graph_code when using torch.export.export contains the "nn_module_stack" dictionary of the first module call of the model, which is an unreadable and long string.

As a prefix it contains a hard-coded string "pre insert_deferred_runtime_asserts" and then the result of f"exported program: {first_call_function_nn_module_stack(gm.graph)}", where the function call returns the dict.

This means that currently at least splitting by ':' will give useable name.

As export requires full graph we will have only one graph, so it will probably not be confusing.

[gilfree]

This should handle #72

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.01%. Comparing base (ee7d231) to head (341dd8a).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
+ Coverage   90.88%   91.01%   +0.12%     
==========================================
  Files          10       10              
  Lines        1547     1547              
==========================================
+ Hits         1406     1408       +2     
+ Misses        141      139       -2     

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[youkaichao]

@gilfree thanks for the fix!