nix: update nixpkgs to the latest & using node20 by default

[hellwolf]

• this also fixes solc-0.8.26 issue for aarch64-darwin (macosx aarch64).

[github-actions[bot]]

Changelog Reminder

Reminder to update the CHANGELOG.md for any of the modified packages in this PR.

• [ ] CHANGELOG.md modified
• [ ] Double check before merge

[codecov[bot]]

Codecov Report

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

Project coverage is 88.44%. Comparing base (69c5856) to head (44c572e). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #2001 +/- ## ========================================== - Coverage 88.55% 88.44% -0.12% ========================================== Files 111 111 Lines 6945 6964 +19 Branches 933 934 +1 ========================================== + Hits 6150 6159 +9 - Misses 793 803 +10 Partials 2 2 ``` | [Flag](https://app.codecov.io/gh/superfluid-finance/protocol-monorepo/pull/2001/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance) | Coverage Δ | | |---|---|---| | [ethereum-contracts](https://app.codecov.io/gh/superfluid-finance/protocol-monorepo/pull/2001/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance) | `94.50% <ø> (-0.26%)` | :arrow_down: | | [sdk-core](https://app.codecov.io/gh/superfluid-finance/protocol-monorepo/pull/2001/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=superfluid-finance) | `88.44% <ø> (-0.12%)` | :arrow_down: | 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=superfluid-finance#carryforward-flags-in-the-pull-request-comment) to find out more.

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XKCD Comic Relif

Link: https://xkcd.com/2001