Let an author carry a note which is not an affiliation

[roytsmart]

aastex.Author could say where someone works and nothing else. AASTeX
reserves \altaffiliation for everything else that needs noting about an
author, and the v7.0 author guide
gives exactly two examples of it:

Authors often have additional information that needs to be noted
(e.g. Hubble Fellow, author is deceased, etc.) in addition to their
affiliation information.

Neither was expressible, so Author gains an altaffiliation field.

aastex.Author(
    name="John Roe",
    affiliation=aastex.Affiliation("Fancy University"),
    altaffiliation="Deceased",
)

\author{John Roe}
\altaffiliation{Deceased}
\email{}
\affiliation{Fancy University}

which typesets as John Roe^1,∗ with ∗Deceased
footnoted at the bottom of the column.

Ordering

The guide is emphatic that the command has to follow \author
immediately, since the footnote symbol attaches to whatever text precedes
it. That is why it is emitted before the \email rather than next to the
affiliations, and test_altaffiliation asserts the position rather than
just the presence of the string.

Testing

A deceased coauthor is added to the document behind
test_generate_archive_compiles, so this goes through a real latexmk
run and would catch the class silently dropping the command. I also
confirmed by hand that the rendered PDF contains the footnote.

The new field is inserted after affiliation rather than appended, which
shifts the positional order of email, orcid, and corresponding.
Every call site in our repos passes these by keyword.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a4b6eb6) to head (725fbe7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #18   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          702       716   +14     
=========================================
+ Hits           702       716   +14     

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

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