Update to latest Nix and fix compilation

Dependencies

• [2] 5T54V3EY Update flake.lock
• [3] HAJZXVXR Use nixFlakes in devShell
• [4] KMQAEXZ2 Build using the nix flake
• [5] M32RT6PS Update flake.{nix,lock}
• [6] GFT3FABQ Update lock file
• [7] HVHW3XPJ Update flake.lock
• [8] JGWFBGDI Update flake.nix
• [9] J5LTAHYV Update flake.nix
• [10] CCPSI3TP Add flake.nix
• [11] 6LB22PZN Add a NixOS container to demo Hydra
• [12] XQLVYZFM Bump flake dependencies
• [13] P3M6UFMP Merge remote-tracking branch 'origin/master' into flake
• [14] 6EAXKZCU Use the overlay from the nix flake
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• replacement in flake.lock at line 7
  [3.97]→[2.0:86](∅→∅)
  − "narHash": "sha256-ALTr2z3J1mE/2OAuEIALIq5pxgADfKvq7rF7gqxT4c0=",
  [3.97]

  [3.86]
  + "narHash": "sha256-ZzR2l1dovxeZ555KXxz7SAXrC72BfaR4BeqvJzRdmwQ=",
• replacement in flake.lock at line 9
  [3.146]→[2.87:181](∅→∅)
  − "url": "github:edolstra/nixpkgs/bcceb882ccdfa818c1e18f4c1e88f2db68964305"
  [3.146]

  [3.338]
  + "url": "github:edolstra/nixpkgs/d37927a77e70a2b3408ceaa2e763b6df1f4d941a"
• replacement in flake.lock at line 12
  [3.371]→[3.241:319](∅→∅)
  − "narHash": "sha256-Y1cdnCNoJmjqyC/a+Nt2N+5L3Ttg7K7zOD7gmtg1QzA=",
  [3.371]

  [3.319]
  + "narHash": "sha256-jdPbZC16ky1nhh1P0E6RGnEjtDofgfbWXFn1v6GyYXA=",
• replacement in flake.lock at line 14
  [3.353]→[3.353:432](∅→∅)
  − "url": "github:NixOS/nix/9cac895406724e0304dff140379783c4d786e855"
  [3.353]

  [3.450]
  + "url": "github:NixOS/nix/0ba8a4e942fbbc6ed71fa3aa76c6f923de3923ee"
• replacement in flake.lock at line 18
  [3.567]→[2.182:260](∅→∅)
  − "narHash": "sha256-ALTr2z3J1mE/2OAuEIALIq5pxgADfKvq7rF7gqxT4c0=",
  [3.567]

  [3.511]
  + "narHash": "sha256-ZzR2l1dovxeZ555KXxz7SAXrC72BfaR4BeqvJzRdmwQ=",
• replacement in flake.lock at line 20
  [3.563]→[2.261:347](∅→∅)
  − "url": "github:edolstra/nixpkgs/bcceb882ccdfa818c1e18f4c1e88f2db68964305"
  [3.563]

  [3.157]
  + "url": "github:edolstra/nixpkgs/d37927a77e70a2b3408ceaa2e763b6df1f4d941a"
• replacement in flake.nix at line 113
  [3.4133]→[3.4133:4161](∅→∅)
  − nlohmann_json
  [3.4133]

  [3.4161]
  + (nlohmann_json.override { multipleHeaders = true; })