chore: update flake.nix

[erics118]

• removes default.nix and flake-compat b/c outdated and flakes are pretty much the standard
• switches from flake-utils to the more modern flake-parts
• update flake.lock
• add rust-analyzer
• removes explicitly including clippy and rustfmt becase they are included with the toolchain
• adds nixfmt as formatter for the flake itself

Checks

• I am happy for maintainers to push small adjustments to this PR, to speed up the review cycle
• I have checked that there are no existing pull requests for the same thing

[github-actions]

Fossier: Manual Review Requested

@erics118 is a new contributor. A maintainer should review this PR before merging.

Score Breakdown

Total Score: 64.6/100 | Confidence: 100% | Outcome: REVIEW

Signal	Value	Score	Weight
account_age	2526	1.00	0.09
public_repos	51	1.00	0.05
contribution_history	51	0.26	0.05
follower_ratio	1.09	0.55	0.05
bot_signals	False	0.50	0.04
open_prs_elsewhere	7	0.12	0.09
closed_prs_elsewhere	6	0.40	0.10
merged_prs_elsewhere	46	1.00	0.08
prior_interaction	2	0.67	0.08
activity_velocity	0	1.00	0.08
pr_content	...	1.00	0.08
commit_email	no_email	0.50	0.04
pr_description	...	0.70	0.05
repo_stars	30058	0.30	0.04
org_membership	0	0.20	0.03
commit_verification	...	1.00	0.04
contributor_stars	10	0.20	0.04

[greptile-apps]

Greptile Summary

This PR updates the Nix flake setup. The main changes are:

• Removes the legacy default.nix flake-compat entrypoint.
• Replaces flake-utils with flake-parts.
• Updates locked Nix inputs.
• Adds rust-analyzer and a Nix formatter output.

Confidence Score: 4/5

This is close, but the flake hash should be fixed before merging.

• The changed toolchain hash can make flake evaluation fail.

• The failure affects normal Nix workflows like build, develop, and flake check.

• The rest of the flake migration looks contained.

• flake.nix needs the toolchain hash padding restored.

Important Files Changed

Filename	Overview
flake.nix	Migrates flake outputs to flake-parts, but the Rust toolchain hash appears to have lost required padding.
flake.lock	Refreshes Nix inputs and swaps flake-utils/flake-compat for flake-parts dependencies.
default.nix	Removes the non-flake compatibility entrypoint.

_{Reviews (1): Last reviewed commit: "chore: update flake.nix" | Re-trigger Greptile}

[erics118]

nix CI will fail until this PR gets added to unstable (probs a few days): NixOS/nixpkgs#525067

[phanirithvij]

Please don't remove flake-compat, flakes are not infact "pretty much the standard" yet for a reason.

[erics118]

Added back the default.nix