Add libzeem output to zeem-feedstock

[eunos-1128]

This pull request adds a new output called libzeem to the zeem feedstock.

zeem is a C++ library, so using a lib-prefixed output name makes the package naming clearer and more consistent with other C/C++ libraries. This change makes the library available as its own output for direct consumption by users and downstream packages.

ping @conda-forge/zeem

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Guidelines for marking packages as broken:

• We prefer to patch the repo data (see here)
  instead of marking packages as broken. This alternative workflow makes environments more reproducible.
• Packages with requirements/metadata that are too strict but otherwise work are
  not technically broken and should not be marked as such.
• Packages with missing metadata can be marked as broken on a temporary basis
  but should be patched in the repo data and be marked unbroken later.
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Checklist:

• I want to mark a package as broken (or not broken):

  • Added a description of the problem with the package in the PR description.
  • Pinged the team for the package for their input.

• I want to archive a feedstock:

  • Pinged the team for that feedstock for their input.
  • Make sure you have opened an issue on the feedstock explaining why it was archived.
  • Linked that issue in this PR description.
  • Added links to any other relevant issues/PRs in the PR description.

• I want to request (or revoke) access to an opt-in CI resource:

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• I want to add a package output to a feedstock:

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  • Added a small description of why the output is being added.