Issue:
build(deps): bump `diesel` to `2.2.3` and `sqlx` to `0.8.1`

## Type of Change
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- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [x] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
This PR updates `diesel` to `2.2.3`, `sqlx` to `0.8.1` and `bigdecimal` to `0.4.5`. `diesel 2.2.3` requires an MSRV of 1.78, and `sqlx 0.8.1` requires an MSRV of 1.80 (at least until https://github.com/launchbadge/sqlx/pull/3459 is merged and a new version is released), so the MSRV had to be bumped to 1.80.

In addition, this PR removes the dependency on the `bigdecimal` crate in `router` and replaces it with `num-traits`, since we were only using a trait from `num-traits` re-exported by `bigdecimal`.

## Motivation and Context
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The updated versions of the dependencies address security vulnerabilities https://github.com/advisories/GHSA-xmrp-424f-vfpx and https://github.com/advisories/GHSA-wq9x-qwcq-mmgf.

## How did you test it?
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N/A

## Checklist
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- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Resolution:
<think>
PR Context:
- Title: build(deps): bump `sqlx` to `0.8.2`
- Merged: 2024-09-11T16:01:14Z
- Files changed: 5 files
- Commits: 2 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [x] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->

This PR bumps the `sqlx` crate to `0.8.2`. This also allows us to drop our MSRV from 1.80.0 to 1.78.0.

## Motivation and Context
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</think>

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