add nix flake

[rupurt]

This adds a Nix flake which provides:

• hermetic development environment for linux & macos
• overlay for Nix projects to import and use iggy binaries and libraries

[coveralls]

Pull Request Test Coverage Report for Build 9535089100

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.945%

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Totals
Change from base Build 9535075094:	0.0%
Covered Lines:	23210
Relevant Lines:	27649

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9538899730

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.002%

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Totals
Change from base Build 9538414138:	0.0%
Covered Lines:	23193
Relevant Lines:	27610

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💛 - Coveralls