feat: store conversion rates to db

[justinenerio]

Changes

stores conversion rates to db cache

Related issues

Fixes #1469

Checklist

• [x] PR is ready for review (if not, it should be a draft).
• [x] PR title follows Conventional Commits guidelines.
• [ ] Screenshots/video added.
• [ ] Tests added.
• [x] Self-review done.

[codecov[bot]]

Codecov Report

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

Project coverage is 77.64%. Comparing base (d8c40bd) to head (8378462). Report is 17 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1526 +/- ## ======================================= Coverage 77.64% 77.64% ======================================= Files 189 189 Lines 4259 4259 ======================================= Hits 3307 3307 Misses 952 952 ``` | [Flag](https://app.codecov.io/gh/espresso-cash/espresso-cash-public/pull/1526/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=espresso-cash) | Coverage Δ | | |---|---|---| | [solana-beta](https://app.codecov.io/gh/espresso-cash/espresso-cash-public/pull/1526/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=espresso-cash) | `77.64% <ø> (?)` | | | [solana-stable](https://app.codecov.io/gh/espresso-cash/espresso-cash-public/pull/1526/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=espresso-cash) | `77.64% <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=espresso-cash#carryforward-flags-in-the-pull-request-comment) to find out more.

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[ookami-kb]

@justinenerio please resolve conflicts

[justinenerio]

@ookami-kb have fixed conflicts