feat: add nix testing with devimint

[alexlwn123]

• Add nix-powered testing harness using Devimint
• This spins up local fedimint infrastructure for testing

Currently leaving as a draft PR, due to flakey behavior with paying lightning invoices.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 34ffcf223810fdc849f4a21c32d654f38cdaf311

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ------------------ | ----- | | @fedimint/core-web | Patch |

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[github-actions[bot]]

Size Change: +57 B (0%)

Total Size: 7.46 MB

Filename	Size	Change
packages/core-web/dist/index.js	2.44 kB	+24 B (+0.99%)
packages/core-web/dist/worker.js	679 B	+33 B (+5.11%)	🔍

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `packages/wasm-bundler/fedimint_client_wasm_bg.wasm` | 3.73 MB | | `packages/wasm-web/fedimint_client_wasm_bg.wasm` | 3.73 MB |

_{compressed-size-action}