Fixed marginal memory leak in singleton class dpctl_capi

[oleksandr-pavlyk]

dpctl_capi ctor initialize all members, dtor resets smart pointers

This addressed accessing uninitialized variables SDL tool warnings.

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• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/1000/index.html

[coveralls]

Coverage remained the same at 81.999% when pulling 0942321 on dpctl_api-ctor-dtor into 457450a on master.

[github-actions]

Array API standard conformance tests for dpctl=0.14.0=py310h8c27c75_10 ran successfully.
Passed: 33
Failed: 801
Skipped: 3138

[github-actions]

Array API standard conformance tests for dpctl=0.14.0=py310h8c27c75_12 ran successfully.
Passed: 33
Failed: 801
Skipped: 3138

[github-actions]

Array API standard conformance tests for dpctl=0.14.0=py310h8c27c75_12 ran successfully.
Passed: 33
Failed: 801
Skipped: 3138

[oleksandr-pavlyk]

Additional scan of this PR by the tool confirmed that access of uninitialized variable warnings and memory leak warnings are gone.

[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞

[github-actions]

Array API standard conformance tests for dpctl=0.14.0=py310h8c27c75_16 ran successfully.
Passed: 33
Failed: 801
Skipped: 3138