Add option to display microseconds.

[oars]

No description provided.

[jonathanj]

Thanks for the PR, I just have 2 comments:

1. Can you name the argument and all its uses use_microseconds (note the plural) instead? This is more idiomatic English, and what I would expect the option to be named as a user
2. Can you add tests to test_cli (integration tests exercising the command line option) and test_render (unit tests exercising the implementation) for the microseconds cases?

[oars]

Done.

[jonathanj]

If I run pytest I see the following test failures, that I don't see on master. Can you take a look at why there are test failures?

======================================================================================== short test summary info =========================================================================================
FAILED src/eliottree/test/test_format.py::TimestampTests::test_local - Failed: NOTE: Incompatible Exception Representation, displaying natively:
FAILED src/eliottree/test/test_render.py::DefaultValueFormatterTests::test_timestamp_field_local - Failed: NOTE: Incompatible Exception Representation, displaying natively:
FAILED src/eliottree/test/test_render.py::DefaultValueFormatterTests::test_timestamp_microseconds - Failed: NOTE: Incompatible Exception Representation, displaying natively:
=============================================================================== 3 failed, 92 passed, 16 warnings in 2.19s ================================================================================

[oars]

Hmmm that's annoying. I was seeing failures locally before my changes which is why I switched some timezone stuff to constants, but clearly that wasn't enough.

I added more explicit mocking of datetime to prevent that now. Could you check if it's good on your side?

[jonathanj]

Is it necessary to mock timezones? The existing tests didn't mock timezones and I don't think microseconds require timezones to function, what were the timezone/mock changes to support?