add polars-lts-cpu and polars-u64-idx variant

[0xbe7a]

Checklist

• [x] Used a personal fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [x] Reset the build number to 0 (if the version changed)
• [x] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

This adds the polars-lts-cpu and polars-u64-idx build variants and closes #186

I have not yet tested how this interacts with the autotick-bot

[conda-forge-webservices[bot]]

Hi! This is the friendly automated conda-forge-linting service.

I wanted to let you know that I linted all conda-recipes in your PR (recipe) and found some lint.

Here's what I've got...

For recipe:

• Selectors are suggested to take a <two spaces>#<one space>[<expression>] form. See lines [15, 16, 17]

For recipe:

• Jinja2 variable references are suggested to take a {{<one space><variable name><one space>}} form. See lines [15].
• You are setting c_stdlib_version below the current global baseline in conda-forge (10.13). If this is your intention, you also need to override MACOSX_DEPLOYMENT_TARGET (with the same value) locally.

[conda-forge-webservices[bot]]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.