* fix: Use monotonic clock to compute durations

In summary, care must be taken when computing durations. Monotonic
clocks are not subject to system clock adjustments or system clock skew.
The difference between any two chronologically recorded time values is
guaranteed to never be negative.

The same guarantee above does not exist for the difference between two
calls to datetime.now() and friends.

More details and rationale see PEP 418.

Resources:

PEP 418 -- Add monotonic time, performance counter, and process time functions
https://www.python.org/dev/peps/pep-0418/

PEP 564 -- Add new time functions with nanosecond resolution
https://www.python.org/dev/peps/pep-0564/

* fix: Remove camelCasing

Co-authored-by: Markus Unterwaditzer <[email protected]>

Turns out some users manually set user.id and other fields in the scope,
and those values get overwritten by integrations.

Glanced over places where we could be inadvertently overwriting user
data and changed to use setdefault to avoid overwriting existing values.

In the product side we don't really want people to search by this tag as
it is far more expensive than the `transaction.status` property which is
indexed separately. By not emitting this tag and only including it in
the trace context we won't end up with poor performing tags for users to
click on.

To workaround get_trace_context() being called multiple times I needed
an additional non-tags place to store the status. I've had to shim the
status back into tags as non-transaction spans expect to have status as
a tag.

Co-authored-by: Markus Unterwaditzer <[email protected]>

* ref: Introduce linter for proper naming conventions

* ref: Document reasons for ignoring lints

* test: Add RQ 1.3 to test matrix

* fix: add fakeredis