Add comparison = "ratio" as shortcut

[strengejacke]

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Copilot review overview

2 open findings

• The test asserts an exact numeric ratio against a hard-coded value, which can be brittle across… · New
• For consistency with the PR title and common usage elsewhere, consider changing 'short-cut' to… · New

What changed in this PR

Adds a new comparison = "ratio" shortcut to estimate_contrasts() / marginal contrasts generation, so users can request pairwise ratios without writing formula syntax.

Changes:

• Add "ratio" as a recognized comparison string and internally map it to ratio ~ pairwise.
• Update formatting logic to treat "ratio" like the formula-based ratio comparison.
• Add NEWS + documentation updates and a new test covering the shortcut.

File	Description
tests/​testthat/​test-estimate_contrasts.R	Adds test asserting comparison="ratio" returns expected columns/value
R/​get_marginalcontrasts.R	Implements "ratio" shortcut mapping and allows "ratio" in validation
R/​format.R	Updates ratio-detection logic to support string "ratio" as well as formulas
R/​estimate_contrasts.R	Documents "ratio" as a supported comparison string and explains behavior
NEWS.md	Announces new comparison="ratio" shortcut
DESCRIPTION	Bumps package version

Files not reviewed (2)

• man/estimate_contrasts.Rd: Generated file
• man/get_emmeans.Rd: Generated file

🧠 Review effort: Lite

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[strengejacke]

exp(coef()) returns an odds ratio, while estimate_contrasts(m, "sex", comparison = "ratio") computes the ratio between two predicted probabilities, i.e. a risk ratio.