Add read only mode

[pedroripper]

This PR allows the user to load a database in "Read only" mode.

Currently, we have two dispatches for PSRI.load_study, one that applies a migration first (if needed), and another that just loads the database.

When applying a migration, the database should not be in "Read only" mode, so for the second dispatch, I have added a boolean parameter (default = false) that sets the loading mode.

So when a user uses

db = PSRI.load_study(PSRI.PSRDatabaseSQLiteInterface(), database_path; read_only = true)

they can only perform reading queries and cannot modify the database.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.93%. Comparing base (818605d) to head (662fcda).
Report is 1 commits behind head on master.

❗ Current head 662fcda differs from pull request most recent head 5f4a551. Consider uploading reports for the commit 5f4a551 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #214   +/-   ##
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  Coverage   82.93%   82.93%           
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  Files          37       37           
  Lines        4226     4226           
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  Hits         3505     3505           
  Misses        721      721           

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[guilhermebodin]

I think that when we use load_db it is also worth it to set a busy timeout.

[guilhermebodin]

It would be a good idea to create a function here to wrap this repeated code.