Internal backend instance renamed to legacy backend

[Raalsky]

Before submitting checklist

• [ ] Did you update the CHANGELOG? (not for test updates, internal changes/refactors or CI/CD setup)
• [ ] Did you ask the docs owner to review all the user-facing changes?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.02%. Comparing base (2ee659c) to head (ffd27ae).

Files	Patch %	Lines
src/neptune/objects/neptune_object.py	0.00%	2 Missing :warning:
src/neptune/attributes/attribute.py	0.00%	1 Missing :warning:
src/neptune/objects/run.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev/2.0 #1846 +/- ## =========================================== - Coverage 79.14% 79.02% -0.12% =========================================== Files 217 217 Lines 9441 9441 =========================================== - Hits 7472 7461 -11 - Misses 1969 1980 +11 ``` | [Flag](https://app.codecov.io/gh/neptune-ai/neptune-client/pull/1846/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai) | Coverage Δ | | |---|---|---| | [macos](https://app.codecov.io/gh/neptune-ai/neptune-client/pull/1846/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai) | `77.47% <42.85%> (ø)` | | | [py3.8](https://app.codecov.io/gh/neptune-ai/neptune-client/pull/1846/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai) | `77.47% <42.85%> (-0.13%)` | :arrow_down: | | [ubuntu](https://app.codecov.io/gh/neptune-ai/neptune-client/pull/1846/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai) | `77.47% <42.85%> (ø)` | | | [unit](https://app.codecov.io/gh/neptune-ai/neptune-client/pull/1846/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai) | `77.47% <42.85%> (-0.13%)` | :arrow_down: | | [windows](https://app.codecov.io/gh/neptune-ai/neptune-client/pull/1846/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neptune-ai#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.