Utilize content addressed binaries and reduce src dl

[johnalotoski]

Overview:

• Decreases initial eval and shell entrance time and download size significantly (see benchmark section)
• Utilizes content addressed pure fetchClosure packages where possible
• Eliminates flake inputs where possible to reduce initial recursive source pulls
• NixOS service only flake references are set to flake = false which is adequate for nixOS module import

Benchmark:

• Quick benchmark test taken before and after this PR for entering an ops shell from a clean cardano-parts nix-garbage-collected system.
• Total file count and download size are determined after having entered the new shell, then exiting and removing the GC roots for the shell and re-running a nix-collect-garbage.
• In the "After PR" part of the comparison, the offchain-metadata-registry-tools binaries and cardano-faucet binary are not included as they are not available in capkgs yet. However, this won't affect the overall comparison significantly as the binaries from capkgs are much smaller/quicker than the alternative use of the upstream flake input due to the flakes recursive input source download, IFD and eval time to arrive at the binary artifact(s).
• Speed test shows ~150 Mbps download bandwidth at the time of testing

Ops shell:
                  Before PR       After PR
DL size (MiB)     8733            644
File count        7894            854
Time              12m:30s         1m:5s

Migration notes:

• Update your .envrc file with this PRs template version, link
• Add a new flake/lib.nix file to your consuming repo, using the contents here, link
• Requires nix 2.17.0 or later (a direnv check with the new .envrc will warn and exit if you don't meet this requirement)
• Requires nix experimental-feature fetch-closure (a direnv check with the new .envrc will warn and exit if you don't meet this requirement)
• Consuming repos needing to override default packages for packages, jobs or entrypoints use should use the flakeModule pkgs config option (perSystem context: config.cardano-parts.pkgs.<...> = ...;) rather than apply flake input overrides since most default package definitions now come from capkgs.