Time to find a replacement for mozilla/rkv

[gbin]

The first issue appear with the project not being actively maintained for any external user: mozilla/rkv#244

Then ... this happens probably out of it as they don't need lmdb internally it got plainly dropped:
mozilla/rkv#239

This is problematic for us because we use it during the build process.

The context for us: This is used for storing the interned string (constant logging string in the codebase coming from debug! info! etc... and assigning to them an unique id to be able to reconstruct the full string offline from the created index (a DB basically) and bincode serialized structured data from the unified logging system of Copper.

We need:

1. a DB that has enough ACID property so we don't duplicate strings or create inconsistent DBs when all the rustc processes are hitting it concurrently
2. something simple: please no Postgres instance for storing u32 -> &str pairs :)
3. something fast, the build is already slow and this feature is not helping.

[gbin]

I spotted the crate heed which is a wrapper around ldmb, might be a 1:1 good candidate