Use fuji as canary testnet, run in Nix shell

[d10r]

This PR is about making workflows less flaky, mainly by avoiding the implicit fetching of additional binaries at runtime (after dependencies were installed):

• Use avalanche-fuji as canary testnet (goerli has become too crowded, tends to timeout)
• Use a Nix shell in workflows (not yet all, but all those building ethereum-contracts)
  • Use the Nix provided solc in hardhat and foundry instead of letting them download at runtime
  • (for truffle we need this and this PR merged before we can do the same)
• Updated the graph-cli dependency to have sepolia support
• Removed the shellcheck npm package - it's just a wrapper which downloads a binary on first invocation, which contributes to flakiness (was observed failing already several times) and isn't great security wise (fetching and executing code at runtime, possibly without any checks of the binary) - instead the script tasks/shellcheck-all-tasks.sh now checks if the binary exists in PATH (provided by Nix shell) and only prints a warning if not.
• Light update of CONTRIBUTING.md - TODO: update the section Releases (seems outdated, not related to this PR though)

[github-actions]

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]

Codecov Report

Patch coverage has no change and project coverage change: +9.60 🎉

Comparison is base (56743df) 88.23% compared to head (8004ee9) 97.84%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1373      +/-   ##
==========================================
+ Coverage   88.23%   97.84%   +9.60%     
==========================================
  Files          86       38      -48     
  Lines        4311     2092    -2219     
  Branches      180        0     -180     
==========================================
- Hits         3804     2047    -1757     
+ Misses        463       45     -418     
+ Partials       44        0      -44     

Flag	Coverage Δ
ethereum-contracts	97.84% <ø> (ø)
sdk-core	?

Flags with carried forward coverage won't be shown. Click here to find out more.

see 48 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[hellwolf]

Thank you for nixifying workflows!

[github-actions]

XKCD Comic Relif

Link: https://xkcd.com/1373