`backend` -> `platform` in `MetaBackend`

[MatteoRobbiati]

As title says.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 48.92%. Comparing base (d91dd13) to head (fc69886).

Additional details and impacted files

[](https://app.codecov.io/gh/qiboteam/qiboml/pull/27?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qiboteam) ```diff @@ Coverage Diff @@ ## main #27 +/- ## ======================================= Coverage 48.92% 48.92% ======================================= Files 8 8 Lines 464 464 ======================================= Hits 227 227 Misses 237 237 ``` | [Flag](https://app.codecov.io/gh/qiboteam/qiboml/pull/27/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qiboteam) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/qiboteam/qiboml/pull/27/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qiboteam) | `48.92% <100.00%> (ø)` | | 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=qiboteam#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/qiboteam/qiboml/pull/27?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qiboteam) | Coverage Δ | | |---|---|---| | [src/qiboml/backends/\_\_init\_\_.py](https://app.codecov.io/gh/qiboteam/qiboml/pull/27?src=pr&el=tree&filepath=src%2Fqiboml%2Fbackends%2F__init__.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qiboteam#diff-c3JjL3FpYm9tbC9iYWNrZW5kcy9fX2luaXRfXy5weQ==) | `100.00% <100.00%> (ø)` | |