pydeephaven py-client testing is not deterministic

[devinrsmith]

py-client testing is non-deterministic due to the fact that it does not pin its dependencies.

Structurally, it extends from a python:3.10 base image and installs a non-frozen set of requirements (requirements-dev.txt).

This is in contrast to py-server / Integration testing, which is based off of ghcr.io/deephaven/server-base:edge, which already has the deephaven-core transitive dependencies installed.

Potential solutions would be to use a frozen set for requirements-dev.txt, or adopt a base image approach for py-client testing.

Discovered due to #5620