ipw 1.3.2

Bug fixes

ipwpoint(): weights.trunc was wrong whenever trunc was set. The lower and upper quantiles were recycled across rows, so every truncated weight was replaced by one of the two bounds. Weights are now clipped at the trunc and 1 - trunc quantiles, and weights between the bounds are left unchanged.
ipwtm() with family = "multinomial" or "ordinal": predicted probabilities are now matched to the observed exposure by level name rather than by column position. 1.3.1 stopped with an error for a two-level exposure, or when an exposure level did not occur among the rows used to fit the models.
ipwpoint() with family = "multinomial" now works for a two-level exposure; 1.3.1 stopped with an error (“Observed exposure levels do not match fitted probability levels”).
Added a test for unstabilized weights (no numerator) with family = "multinomial" and "ordinal" in ipwpoint(). These failed in 1.3.0 and were fixed by the 1.3.1 rewrite (#3, @adcascone).
ipwtm() with type = "first" and family = "multinomial" / "ordinal": a switch is again defined as the first record at any level other than the lowest level in the whole data set, as in ipw <= 1.2.1.1. In 1.3.1 the reference level was chosen separately for each subject.

ipwtm() now checks that all model variables exist and contain no missing values, and that a binomial/survival exposure is coded 0/1, with clear error messages instead of errors from inside glm() / coxph().
ipwtm() with family = "survival" now stops with a clear message when a formula contains strata(), which is not supported.
Fitted models returned in num.mod / den.mod no longer carry an inlined copy of the data in their call, so printing them is readable again.
ipwpoint() and ipwtm() share one set of internal helpers for argument checks, formula construction, probability extraction and truncation.
Removed blanket import() of whole packages; all calls use pkg::fun. methods is no longer imported.

Test suite expanded: exact checks of truncation, row-order invariance, two-level multinomial vs binomial equivalence, and error messages.
New regression test against ipw 1.2.1.1 (reference weights created with data-raw/make-regression-fixtures.R).

Core Refactoring (ipwtm, ipwpoint, ipwplot, tstartfun):
- Improved defensive input validation, parameter checking, and error messages across all core functions.
- Modernized formula construction (as.formula()) to eliminate fragile eval(parse(text = ...)) string manipulations.
- Fixed variable symbol evaluation issues when passing variables as function arguments rather than raw names.
- Modularized ipwtm into dedicated family modeling engines (binomial, survival, multinomial, ordinal, gaussian).
- Replaced manual survival hazard step-differencing with continuous baseline hazard interpolation using survival::basehaz and stats::approx.
- Refactored tstartfun to use safe column evaluation and direct vector lag logic (c(-1, t[-length(t)])).
Test Suite Expansion:
- Upgraded testthat suite to 3rd edition specs, expanding coverage for multinomial, ordinal, gaussian, unstabilized models, weight truncation, and invalid parameter rejection.