Improve error messages for vidyut.kosha

[akprasad]

If the vidyut_kosha crate fails, our vidyut.kosha wrapper passes through the raw Rust error and doesn't give much insight on how to correct the error.

This is poor UX. In addition to improving the upstream error messages, we should provide informative messages here.

Errors to test:

• Could not create builder
• Could not insert key (out of order)
• Could not insert key (too many duplicates)
• Could not create kosha
• Could not load kosha (file doesn't exist)
• Could not load kosha (file is malformed)