Size: separate data_length and index_length

Feature Request

• Yes, I reviewed the contribution guidelines.

Especially on larger sites, and with DB optimization (i.e. additional indexes), indexes can be quite big already on its own. Calculating data and index sizes together skew things slightly.

Here's an example of one site

Data total: ~3.43 GB
Index total: ~2.80 GB
Grand total: ~6.23 GB

Describe the solution you'd like

At least when using an output format that doesn't just give the size as a number, data and index should be displayed separately. At least it should be clearly documented that index sizes are counted to tally.

For example with --human-readable instead of

+------+------+
| Name | Size |
+------+------+
| wdb  | 7 GB |
+------+------+

return could be

| Name | Data    | Index   | Total   |
|------|---------|---------|---------|
| wdb  | 3.43 GB | 2.80 GB | 6.23 GB |

There's currently also slight rounding issue where 6.23 GB becomes 7 GB.

Start at the database size reporting path used by the --human-readable output and inspect how data and index sizes are currently combined and rounded. Done means the output separates Data, Index, and Total while preserving the combined total and avoiding the demonstrated rounding discrepancy.