Allow an author to have more than one affiliation

[roytsmart]

Problem

Author.affiliation accepted exactly one Affiliation and dumps() emitted a single \affiliation command, even though AASTeX is happy with several per author.

The usual convention when an author has changed institutions is to list the organization where the work was done, followed by their present one. That was impossible to express.

Changes

Author.affiliation now accepts either an Affiliation or a list of them, and one \affiliation command is emitted for each:

aastex.Author(
    name="Laurel Rachmeler",
    affiliation=[
        aastex.Affiliation("NASA Marshall Space Flight Center"),
        aastex.Affiliation("NOAA National Centers for Environmental Information"),
    ],
)

\author{Laurel Rachmeler}
\email{}
\affiliation{NASA Marshall Space Flight Center}
\affiliation{NOAA National Centers for Environmental Information}

The new Author.affiliations property always returns a list, so callers never have to check which form was given. Passing a single Affiliation behaves exactly as before.

Testing

The TestAuthor parametrization gains an author with two affiliations, and a new test asserts that the number of \affiliation commands matches the number given and that each name appears. Also compiled a document with a two-affiliation author and confirmed both institutions appear in the resulting PDF. Suite: 122 passing, coverage 100%.

🤖 Generated with Claude Code

https://claude.ai/code/session_01BYjDL98znSud1yFh9chnkP

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (d493b15) to head (2793981).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files            4         4           
  Lines          642       673   +31     
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+ Hits           642       673   +31     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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