build: replace nixpkgs-fmt with nixfmt-rfc-style #17429

Job	Run time
Build C library (ubuntu-latest)	2m 36s
cargo deny	31s
Build C library (macos-latest)	7m 4s
Rust doc comments	21s
Lint Rust	7m 37s
Check if node constants are up to date	4s
Check provider database	4s
Python lint	15s
Build deltachat-rpc-server (ubuntu-latest)	7m 29s
Rust tests (ubuntu-latest, 1.83.0)	9m 16s
Rust tests (windows-latest, 1.83.0)	22m 35s
Rust tests (macos-latest, 1.83.0)	7m 45s
Rust tests (ubuntu-latest, 1.81.0)	9m 22s
Build deltachat-rpc-server (macos-latest)	1m 57s
Build deltachat-rpc-server (windows-latest)	19m 49s
CFFI Python tests (ubuntu-latest, 3.13)	5m 4s
CFFI Python tests (macos-latest, 3.13)	4m 54s
CFFI Python tests (ubuntu-latest, pypy3.10)	7m 29s
CFFI Python tests (macos-latest, pypy3.10)	5m 54s
CFFI Python tests (ubuntu-latest, 3.7)	6m 42s
JSON-RPC Python tests (ubuntu-latest, 3.13)	1m 49s
JSON-RPC Python tests (macos-latest, 3.13)	1m 51s
JSON-RPC Python tests (windows-latest, 3.13)	2m 53s
JSON-RPC Python tests (ubuntu-latest, pypy3.10)	2m 2s
JSON-RPC Python tests (macos-latest, pypy3.10)	2m 11s
JSON-RPC Python tests (ubuntu-latest, 3.7)	1m 26s
	2h 19m 0s

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