Unify eslint configurations

[Tellus]

Updating the eslint configuration ended up requiring me to migrate everything at once, as well as the prettier configurations, so this PR should manage to close #44, #43, #42, #41, #40, #39, #38, #37, #36, #35, #34, #33, #32, #31, #30, and #3 (apologies for the massive spam).

A few notes on the changes:

• eslint has introduced a new config format, "flat" configs. The notion is to stop using .eslintrc files (which use strings to point to plugins/configurations), and move to a eslint.config.js file that imports the packages directly and passes the plugin objects back to eslint. It seems like a reasonable change, but some of the plugins currently in use have not yet added support for flat configs (see ESLint Flat Config Support typescript-eslint/typescript-eslint#7694). As a result, the new monorepo configuration does not use flat configs, but it should be a priority to switch over once the plugins we depend on have added support.
• a good deal (but not all) packages had set the rule sonarjs/no-duplicate-string. I've worked on the assumption that this was because some eslint configs had simply not had the rule added, and put it in the monorepo root config. This can be overridden if necessary.
• it looked like my VSCode was giving wonky eslint results without a prettier configuration in the root folder, so created one and removed all the separate configs (they are all identical).

When merging this PR, consider squashing first - there are several intermediary commits that I think would just pollute the history

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[Tellus]

A changeset was omitted on purpose. None of the changes in the PR affect package functionalities and are functionally indistinct from those already published.