Fix deprecated CONCENTRATION_* constants (use UnitOfDensity/UnitOfRatio)

[Wiggum127]

Breaking change

Proposed change

Fixes #459

Replaces the deprecated CONCENTRATION_MICROGRAMS_PER_CUBIC_METER and
CONCENTRATION_PARTS_PER_MILLION constants with their UnitOfDensity /
UnitOfRatio equivalents, ahead of removal in HA Core 2027.8.

No functional change — same units, just the current constant names.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Deprecated constants CONCENTRATION_MICROGRAMS_PER_CUBIC_METER / CONCENTRATION_PARTS_PER_MILLION (removed in HA Core 2027.8) #459
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• The code has been formatted using Ruff (ruff format custom_components/victron)

[Wiggum127]

I don't have permission to add a label myself (no write access to this repo) — could you add bugfix or whichever fits so the label-check passes? Thanks!