Add compile-time check for terminating decimal

See this comment:

https://github.com/kowainik/membrain/blob/0ed5b57f473f4fa3b3d21e5b1c4773ac40ee3e51/src/Membrain/Memory.hs#L52

Open the linked comment in src/Membrain/Memory.hs at line 52 and read the surrounding type-level memory-unit definitions first. Determine the intended compile-time check for terminating decimal values, then verify that invalid values are rejected and valid terminating decimals remain accepted using the repository's existing checks.

Written by the indexing model from the issue text.