[Bug] v.to.rast writing 0 categories in metedata when use=cat

[petrasovaa]

Describe the bug
When rasterizing with use=cat and then running r.info, you get (see Number of Categories):

...
 |   Type of Map:  raster               Number of Categories: 0               |
 |   Data Type:    CELL                 Semantic label: (none)                |
 |   Rows:         226                                                        |
 |   Columns:      220                                                        |
 |   Total Cells:  49720                                                      |
 |        Projection: Lambert Conformal Conic                                 |
 |            N:     226800    S:     220020   Res:    30                     |
 |            E:     639030    W:     632430   Res:    30                     |
 |   Range of data:    min = 696  max = 1466 
...

This is confusing, you would expect the number of categories to be > 0.
This was originally reported by a user.

Additional context
AFAIU, this used to work until 8a1cd94, which disabled the category writing due to performance reasons. So I am not sure how to address this.

[Abhi-d-gr8]

Hi @petrasovaa ,
I opened a PR:#7019
Which restores category metadata for use=cat by using Rast_set_cats_fmt() instead of writing per-category rules. This avoids the performance issues of enumerating categories while fixing the confusing categories=0 output in r.info.