dockerTools: Support mounting images with more than 16 layers (backport to 24.11)

[charles-dyfis-net]

24.11 variant of PR #392422, both addressing #392421.

When a Docker image contains more than 16 layers, the mount -t overlay command run to combine those into a single filesystem view fails.

To address this, we now loop in batches of 16 mount points until we've combined all layers into a single mount.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[wolfgangwalther]

At first glance the changes in here look exactly the same as in the PR to master. We don't need two manually created PRs: We can merge the one to master, and then automatically backport via label.

Alternatively, you'll need to manually cherry-pick the commit once the PR is merged to master with the -x option.