Add `BorderType` enum to bmsmsd

[dyceron]

Adds an enum to BorderType in the bmsmsd. It's kinda weird and a lot, but it covers all of the tile borders.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 74.14%. Comparing base (71851d0) to head (2802c6a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #139 +/- ## ======================================= Coverage 74.13% 74.14% ======================================= Files 63 63 Lines 3155 3156 +1 ======================================= + Hits 2339 2340 +1 Misses 816 816 ```

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[dyceron]

this should be a FlagsEnum with just 8 entries (4 normal edges, 4 hidden edges)

You mean instead of the big enum? Idk what that is.

[duncathan]

https://construct.readthedocs.io/en/latest/api/mappings.html

[dyceron]

I sorta understand but what to map the enum values to is confusing

[duncathan]

the values you have for 1, 2, 4, 8, 16, 32, 64, and 128