fix: multi-line facet panel strip labels for facet_grid and facet_wrap (#262)

[ANAMASGARD]

Fixes #262 — animint2 currently joins multi-variable facet strip labels onto one line (cyl: 4; am: 0). This PR makes them render on separate lines like ggplot2 does.

Root cause

Facet type	Bug location	Current join
facet_grid	R/z_facets.R build_strip()	"; "
facet_wrap	R/z_facets.R getStrips.wrap()	", "

draw_strip() in animint.js renders one flat <text> node — no <tspan> support today.

Two-commit structure

Commit 1 (this commit) - failing test only

• Adds test-renderer1-facet-multiline.R
• Checks 12 <tspan> elements across 6 panels × 2 variables for both
  facet_grid and facet_wrap
• Currently fails: length(labels) == 0 (no tspans exist yet)

Commit 2 — implementation

• R/z_facets.R: change collapse = "; " / ", " -> collapse = "\n"
• inst/htmljs/animint.js: split on \n, render each line as <tspan>

[codecov]

Codecov Report

❌ Patch coverage is 85.48387% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.07%. Comparing base (426295c) to head (66566d8).

Files with missing lines	Patch %	Lines
inst/htmljs/animint.js	85.18%	8 Missing ⚠️
R/z_facets.R	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
+ Coverage   73.03%   73.07%   +0.04%     
==========================================
  Files         164      164              
  Lines        8840     8887      +47     
==========================================
+ Hits         6456     6494      +38     
- Misses       2384     2393       +9     

Flag	Coverage Δ
javascript	81.25% <85.18%> (-0.01%)	⬇️
r	69.15% <87.50%> (+<0.01%)	⬆️

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[tdhock]

thanks, can you please post a screenshot using the new code?

[ANAMASGARD]

Sir @tdhock I have posted screenshot using new code, please also review all the PR's I have raised (when you get time ) they all need review once done I can move forward , Thanks .

• Left: facet_grid(cyl + am ~ .) = row strips show cyl and am on separate lines instead of being joined with ;.
• Right: facet_wrap(~ cyl + am) = top strips also split onto two lines instead of being joined with ,.
  Both facet paths now match ggplot2's multi-line strip rendering. The test test-renderer1-facet-multiline.R passes locally (12 elements found across 6 panels × 2 variables).

[tdhock]

thanks. can you please revise so that the multi-line facet title does not go into the plotting area? (the height / width of the plotting area size needs to be a function of how many lines in the title)

[ANAMASGARD]

Sir @tdhock Follow-up on your overlap comment I have added geometry tests and fixed strip placement so multi-line titles stay in the strip band, not on the plot. CI was red on the test-only commit (expected), then green after the fix.
Could you review again this PR and give feedback thanks .

[tdhock]

please resolve conflict and post a new screenshot?