chore(backup): allow backups on a live database (#2986)

## Linked Issues/PRs
<!-- List of related issues/PRs -->
- needed for some infra work with @tirkesi

## Description
<!-- List of detailed changes -->
Small changes
- when we open a database for backup, we now open in read-only mode,
allowing database writes to occur while the backup is in progress
- increase parallelism for the backup process, improving performance

## Checklist
- [x] Breaking changes are clearly marked as such in the PR description
and changelog
- [x] New behavior is reflected in tests
- [ ] [The specification](https://github.com/FuelLabs/fuel-specs/)
matches the implemented behavior (link update PR if changes are needed)

### Before requesting review
- [ ] I have reviewed the code myself
- [ ] I have created follow-up issues caused by this PR and linked them
here

### After merging, notify other teams

[Add or remove entries as needed]

- [ ] [Rust SDK](https://github.com/FuelLabs/fuels-rs/)
- [ ] [Sway compiler](https://github.com/FuelLabs/sway/)
- [ ] [Platform
documentation](https://github.com/FuelLabs/devrel-requests/issues/new?assignees=&labels=new+request&projects=&template=NEW-REQUEST.yml&title=%5BRequest%5D%3A+)
(for out-of-organization contributors, the person merging the PR will do
this)
- [ ] Someone else?