Fix missing denominator degrees of freedom in lmerTest ANOVA reports

[Copilot]

When using lmerTest::lmer() models with report(anova()), the output was missing denominator degrees of freedom in the F-statistic. Instead of showing F(1, 21.92) = 62.20, it only showed F(1) = 62.20.

Problem
The issue occurred because report_statistics.aov() only checked for denominator degrees of freedom in:

1. "Residuals" rows in the Parameter column (for regular ANOVA tables)
2. "DoF_Residuals" columns (legacy format)

However, lmerTest provides denominator degrees of freedom directly in a df_error column for each parameter, which wasn't being checked.

Solution
Added a third condition to check for the df_error column in the parameters table:

# Before (incomplete logic)
if (!is.null(DoF_residual)) {
  text <- paste0(text, ", ", insight::format_value(DoF_residual, protect_integers = TRUE))
} else if ("DoF_Residuals" %in% names(parameters)) {
  text <- paste0(text, ", ", insight::format_value(parameters$DoF_Residuals, protect_integers = TRUE))
}

# After (complete logic)  
if (!is.null(DoF_residual)) {
  text <- paste0(text, ", ", insight::format_value(DoF_residual, protect_integers = TRUE))
} else if ("DoF_Residuals" %in% names(parameters)) {
  text <- paste0(text, ", ", insight::format_value(parameters$DoF_Residuals, protect_integers = TRUE))
} else if ("df_error" %in% names(parameters)) {
  text <- paste0(text, ", ", insight::format_value(parameters$df_error, protect_integers = TRUE))
}

Example

library(lmerTest)
library(report)

m <- lmerTest::lmer(mpg ~ wt + (1| gear), data=mtcars) 
report(anova(m))

# Before: F(1) = 62.20, p < .001 (missing denominator df)
# After:  F(1, 21.92) = 62.20, p < .001 (includes denominator df)

The fix preserves all existing functionality for regular ANOVA models while properly supporting lmerTest models that provide Satterthwaite or Kenward-Roger denominator degrees of freedom.

Fixes #453.

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