Improve facet error messages in animint2dir

[ANAMASGARD]

FIXES #168

What's broken

viz <- list(
  plot = ggplot() + 
    facet_wrap(. ~ Species) +  # formula notation
    geom_point(aes(x, y), data = iris)
)
animint2dir(viz) 

• Current error:
  Error: At least one layer must contain all variables used for facetting

Doesn't tell you what's wrong or how to fix it.

• Workaround that works:
  facet_wrap("Species") # string notation works fine

What I am fixing

1. Detect when formula notation is used in facets
2. Give clear error telling user to use string notation instead
3. Fix happens in animint2dir() - animint2-specific code only

Next commit will add the fix to make tests pass.

[ANAMASGARD]

Before :-

Error: At least one layer must contain all variables used for facetting

After :-

Error: Facet variable not found in data: MissingVar
Available columns: Sepal.Length, Sepal.Width, Petal.Length, Petal.Width, Species
Use string notation like facet_wrap("var") instead of formula notation facet_wrap(. ~ var) ```

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.04%. Comparing base (a4220df) to head (d719de1).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #285      +/-   ##
==========================================
+ Coverage   73.02%   73.04%   +0.02%     
==========================================
  Files         164      164              
  Lines        8837     8845       +8     
==========================================
+ Hits         6453     6461       +8     
  Misses       2384     2384              

Flag	Coverage Δ
javascript	81.23% <ø> (ø)
r	69.18% <100.00%> (+0.04%)	⬆️

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[tdhock]

No obvious timing issues in HEAD=fix-168-facet-error-message

Generated via commit c1877ef

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	2 minutes and 12 seconds
Installing different package versions	27 seconds
Running and plotting the test cases	3 minutes and 29 seconds

[ANAMASGARD]

Sir @tdhock The 2 failing tests in JS_coverage are in test-compiler-ghpages.R (GitHub Pages tests), not related to this PR. This is the same race condition issue where parallel CI jobs conflict over the shared test repository.

All facet-related tests pass:

• R_coverage: 2096+ tests passed
• CRAN: passed
• My 3 new facet error message tests pass

The fix is working correctly. Please review and give your feedback Sir .

[ANAMASGARD]

Also Sir @tdhock atime performance tests / comment job failing actually has nothing to do with this PR :

• It installs animint2 from an old baseline commit to compare performance before and after my changes
• The baseline commit it is using is 352f7e1 (version 2025.9.16)

Where it crashes:

It crashes during R CMD INSTALL of that old commit with this error:

Error: geom_dotplot.Rd:125: processing build-stage \Sexpr code failed:
Error: No geom called GeomDotplot.
ERROR: installing Rd objects failed
Error in atime_versions_install(...) :
  '/opt/R/4.6.0/lib/R/bin/R' CMD INSTALL returned error status code 1 

Why does this happen:

• That old commit's geom_dotplot.Rd has a \Sexpr line that looks up GeomDotplot at build time
• GeomDotplot was removed from animint2 after that commit
• So the old doc file now breaks when installed under R 4.6.0
• The current man/geom_dotplot.Rd on master is already fixed — this is only broken in that old commit

My changes are never even reached — the job dies at install time before running any performance tests.

There is also this warning in the log:

Warning: CRAN version=2025.10.17 but installed version=2026.2.28
fix via install.packages('animint2') 

This is an infrastructure/CI issue, not a code issue. Can you please tell what should I do not it is happening in my other PR's also .