Pooldose: Add sensors for water meter

[lmaertin]

Breaking change

Proposed change

• Add sensors for water meter
• Fixed duplicated flow_rate sensor
• Adapted tests as well

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 #
• This PR is related to issue:
• Link to documentation pull request: Add sensor for water totalizer home-assistant.io#42027
• Link to developer documentation pull request:
• Link to frontend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[Copilot]

Pull request overview

This PR adds support for water meter sensors to the Pooldose integration and fixes a unit handling issue that caused the flow_rate sensor to be duplicated. The changes enable users to track both permanent and resettable water meter readings from their Seko PoolDose devices.

Key Changes

• Added two new water meter sensors: total (permanent) and resettable volume measurements
• Fixed unit mapping to be case-insensitive by converting device units to uppercase before lookup
• Updated test fixtures and snapshots to reflect the new sensors

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
homeassistant/components/pooldose/sensor.py	Added two new sensor entity descriptions for water meters with VOLUME device class and dynamic unit handling; updated unit mapping to convert to uppercase
homeassistant/components/pooldose/const.py	Updated UNIT_MAPPING dictionary to use uppercase keys and added volume unit mappings (L, M3)
homeassistant/components/pooldose/strings.json	Added translation strings for the two new water meter sensors
homeassistant/components/pooldose/icons.json	Added icon definitions (mdi:counter) for both water meter sensors
tests/components/pooldose/fixtures/instantvalues.json	Added test data for water meter sensors and fixed flow_rate unit casing
tests/components/pooldose/snapshots/test_sensor.ambr	Added snapshot entries for both new water meter sensor entities and their expected states