SQLite cache: Use SQLite write-ahead logging for better concurrency

[amotl]

Problem

@edgarasg reported there is still a problem with the SQLite-based cache and concurrent access.

• https://github.com/panodata/grafana-wtf/issues/111#issuecomment-2058840165

Solution

@JWCook informed us about the wal=True argument to requests-cache' Session class/mixin, effectively enabling SQLite write-ahead logging, allowing read operations to not block writes.

• https://github.com/panodata/grafana-wtf/issues/111#issuecomment-2067705159

[1] https://sqlite.org/wal.html

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.17%. Comparing base (756e395) to head (3fa8a80).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #136 +/- ## ======================================= Coverage 87.17% 87.17% ======================================= Files 9 9 Lines 1076 1076 ======================================= Hits 938 938 Misses 138 138 ``` | [Flag](https://app.codecov.io/gh/panodata/grafana-wtf/pull/136/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=panodata) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/panodata/grafana-wtf/pull/136/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=panodata) | `87.17% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=panodata#carryforward-flags-in-the-pull-request-comment) to find out more.

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