feat: add direction support for right and down

[M-Hawkins]

Thanks for putting this together, this is the lightweight functionality I was looking for!
For some of my 'live' tables (i.e. continuously appended to) having a calculated expression remain at the top and/or left hand side fits better.
This pr adds the two remaining directions to enable that behavior.

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Raw table:

| a    | b    | c    | d    | e   |
| ---- | ---- | ---- | ---- | --- |
|      | 123  | SUMv |      |     |
| SUM> | 456  | 123  |      |     |
|      | SUM^ | 456  | SUM< |     |
| SUM> | 234  | SUM> | 789  | 456 |
|      | SUM^ | 789  |      |     |

Live preview:

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Note: I haven't exhaustively tested the other operation types or optional args, only what's pictured here.

[eatcodeplay]

Hey @M-Hawkins sorry for the late reply to this. Had health issues, but i'm back now. 💪
I just released 0.2.4 which fixed some other things and has changed certain things that affect your PR.

If you could have a look at it, then i'll gladly merge this as soon as possible (and after doing some more testing) ❤️