Use constants for translation keys and rename latency time to latency

[elmurato]

Proposed change

Code cleanups as a preparation for PR #97837:

• Use constants for translation keys.
• Rename "latency time" to "latency".
• Remove unused constant KEY_SERVERS.
• Fix typo in a comment.

Note:
NAME_LATENCY is still defined as "Latency Time", and not "Latency". This will be fixed in PR #97837 as this affects the entitiy unique ID.

Once this PR is accepted and merged, PR #97837 will be rebased upon these changes and continued.

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• Dependency upgrade
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[joostlek]

What do you think about moving all these sensors into SensorEntityDescriptions? Since you might be adding bedrock support, you will add more sensors, so that would make that easier and this code way cleaner

[elmurato]

What do you think about moving all these sensors into SensorEntityDescriptions? Since you might be adding bedrock support, you will add more sensors, so that would make that easier and this code way cleaner

Interesting, didn't know about it before, thanks! With that the code will be cleaner, agreed. But would it be OK for you, if I implement it after this PR and PR #97837? After those PRs and before tackling Bedrock support I wanted to switch to the DataUpdateCoordinator. Looks like adding SensorEntityDescriptions before that would make sense.

[gjohansson-ST]

Thanks @elmurato 👍