[Feature]: Adapt Totals check to account for filter_default entries

### Description

The Totals check will currently always flag a warning if a team is using a custom filter default. The test should be adapted to search for the custom filter default where present rather than Total. And if a custom filter default is set, then it should error if it's then not present in the data.

### Use case

As an analyst, I want to know that I'm using filter_default correctly so that the relevant EES functionality works.

### Why this is important

Analysts will trust the screener less if they keep on getting false warnings around Total when they're actually using a custom default.

### Additional Context

N/A

Locate the Totals check and its existing test, then read how filter_default and Total are currently searched in the data. Update the test behavior so a custom filter_default is used when present and an error is raised when that configured value is absent from the data. Run the relevant test suite to verify that valid custom defaults no longer produce false warnings.

Written by the indexing model from the issue text.