* testing: refactored logs directory management
* content: fixed index mutex to be shared across all write sessions
added mutex protection during writecontent/refresh race
* testing: upload log artifacts
* content: bump revision number after index has been added
This fixes a bug where manifest manager in another session for
the same open repository may not see a content added, because they
will prematurely cache the incomplete set of contents.
This took 2 weeks to find.
* manifest: improved log output, fixed unnecessary mutex release
* testing: rewrote stress test to be model-based and more precise
* cli: Added --max-examples-per-bucket flag to 'kopia snapshot estimate'
Added and cleaned up a bunch of unit tests.
Fixes#1054
* cli: misc tests to increase code coverage of the cli package
* ci: move code coverage run into separate GH job
