Fix logic managing dll search path and path when initializing dpctl

[ndgrigorian]

This PR refactors some logic in dpctl managing the DLL search path, also adding the dpctl __init__.py directory to the PATH, matching the logic in dpnp, in an attempt to fix dpctl being imported from virtual environments failing to see devices or find SYCL dlls

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[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/2130/index.html

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_93 ran successfully.
Passed: 1115
Failed: 6
Skipped: 119

[coveralls]

coverage: 85.902% (+0.02%) from 85.878%
when pulling 2680eb8 on fix-dpctl-import-from-venv-windows
into 3381d14 on master.

[antonwolfy]

Thank you @ndgrigorian for resolving the issue

[github-actions]

Array API standard conformance tests for dpctl=0.21.0dev0=py310h93fe807_93 ran successfully.
Passed: 1115
Failed: 6
Skipped: 119