feat: add Nix flake and direnv support

[VVKot]

Which issue does this PR close?

Happy to file an issue if needed!

Rationale for this change

DataFusion requires protobuf and OpenSSL installations to compile. Existing instructions only cover FHS-compliant systems.

What changes are included in this PR?

• Nix flake with protobuf, openssl, and pkg-config to avoid configuring the paths manually
• Nix flake lockfile
• integration with https://github.com/nix-community/nix-direnv to automatically load the flake when entering source code directory

What is the testing strategy for this PR?

I have confirmed DataFusion now successfully compiles without having protobuf or OpenSSL installed globally. Would appreciate confirmation that this also works for other Nix[OS] developers!

Are there any user-facing changes?

No.

Other considerations

I chose to track the stable channel to minimize the risk of flake breaking. I chose to check-in the flake lock for reproducibility - note that this means it will need to be periodically bumped.

This flake could be further extend to include other "supporting" packages that DataFusion relies on for development, such as uv -- omitted those for simplicity of the PR / to not have to decide what goes into flake VS not now.

I appreciate this is yet another developer-facing file that needs to be maintained, and the project already has a devcontainer setup. However, this provides a quick start for all developers using Nix[OS], without forcing them to accept overhead of a Docker container, or figuring out the native libraries installation themselves.

If nothing else -- every time I git clone a project that has flake + direnv integration and automatically sets up a Nix shell that "just works", it makes my day a little bit and makes me that much more likely to consider contributing. :) I want the same experience for all (future) DataFusion contributors out there!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.64%. Comparing base (95a1961) to head (c4752f3).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26005      +/-   ##
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- Coverage   82.64%   82.64%   -0.01%     
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  Files        1147     1147              
  Lines      445502   445502              
  Branches   445502   445502              
==========================================
- Hits       368179   368169      -10     
- Misses      54969    54974       +5     
- Partials    22354    22359       +5     

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[kumarUjjawal]

Thank you @VVKot

The changes look good to me

[VVKot]

@kumarUjjawal are we good to merge here then?

[kumarUjjawal]

@kumarUjjawal are we good to merge here then?

Yes, thank you for the ping.

[kumarUjjawal]

Thank you @VVKot for your contribution!