Improve options for partitioning a single light from an addressable led array

**Describe the problem you have/What new integration you would like**

When using the partition light platform, include an option to segment a single LED. For example, using an array of addressable led lights as different status lights in a project, you must include segment start and end number. A shorthand option would make the yaml easier to write.

**Please describe your use case for this integration and alternatives you've tried:**

Segmenting an led is already possible, for example:
```
- platform: partition
id: light_high
segments:
- id: light_bus_board
from: 3
to: 3
```

This request is to add an option in the segments section to replace from and to when they are the same. For example:
```
- platform: partition
id: light_high
segments:
- id: light_bus_board
single: 3
```

**Additional context**

Start at the partition light platform and its segment configuration, then trace how the existing from and to values are parsed and applied. Done means the segments section accepts a single option equivalent to matching from and to values, while preserving the existing syntax and behavior.

Written by the indexing model from the issue text.