Added on-disk MongoDB compatible MontyStore

[utf]

In my opinion, one missing component of the maggma stores is a persistent on disk store that can be accessed simultaneously from multiple python processes. Think an almost fully formed MongoDB instance but hosted locally on the file system. I think this is what #507 is hinting towards.

In this PR I've implemented a store based on the MontyDB backend. This provides a MongoDB interface to several on disk stores including:

• sqlite: Uses an sqlite database to store documents.
• lightning: Uses Lightning Memory-Mapped Database (LMDB) for storage. This can provide fast read and write times but requires lmdb to be installed (in most cases this can be achieved using pip install lmdb).
• flatfile: Uses a system of flat json files. This is not recommended as multiple simultaneous connections to the store will not work correctly.

The data is stored in a folder on disk controlled by the database_path option. Multiple databases and collections are stored as different files.

I've added full tests and MontyDB as an optional requirement. @davidwaroquiers you may be interested in this.

[codecov]

Codecov Report

Merging #514 (a0c5e59) into main (6de8739) will increase coverage by 0.04%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main     #514      +/-   ##
==========================================
+ Coverage   88.79%   88.84%   +0.04%     
==========================================
  Files          40       40              
  Lines        2696     2743      +47     
==========================================
+ Hits         2394     2437      +43     
- Misses        302      306       +4     

Impacted Files	Coverage Δ
src/maggma/stores/mongolike.py	85.75% <91.66%> (+0.92%)	⬆️

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[shyamd]

Is there any reason to not just replace the monogmock MemoryStore based implementations with this montydb variant?

[utf]

Maybe. The existing memory store is based on mongomock which I think is a more feature complete replica of pymongo. For example, it implements bulk_write whereas MontyDB does not.

[munrojm]

@utf I agree with your sentiment, and like this implementation. Are you good for me to merge?

[utf]

Yeah all good from me. I've been using this and seems to work well.

[munrojm]

Sounds good!