Implementation of the context timing

[sebastiencs]

This exposes the context stats on the RPC endpoint GET /stats/context.

Data is stored in a sqlite database from the protocol runner process, where statistics are computed.
When the RPC endpoint is called, it reads from that sqlite file and formats it according to the example JSON I got.
Note that the endpoint expose only tezedge stats, even though irmin ones are in the db.

• I'm not sure what should be the path of the database file ?
• There is no tests yet on the RPC endpoint, should I include an already filled sqlite database in the repository ? So that the tests would just read from it

[tizoc]

@sebastiencs overall it looks good, I left some comments.

Also, I think it would be better to use the rusqlite crate, seems to have a more convenient API, more users, support for transactions, etc. Some of the things may not be needed now but if we extend this to be a replacement for the current context actions storage, those are going to be come useful (because those features will help with optimizing things more).

[tizoc]

Oh and about your questions

I'm not sure what should be the path of the database file ?

Good question. I am not sure yet, add some default and we can figure it out later.

There is no tests yet on the RPC endpoint, should I include an already filled sqlite database in the repository ? So that the tests would just read from it

For the test you can initialize the Sqlite store in-memory, and insert whatever values you want to it, no need for an on-disk file.

[tizoc]

In-memory SQlite database: https://sqlite.org/inmemorydb.html