.model name clash when forecasting from components()

Hi,

When forecasting off the back of a components() call, you run into an issue because there is already a '.model' column.

I ran into this when running through Chapter 8, Exercise 10 in FPP3. Of course I could be doing this in the wrong manner, so apologies for this issue if that is the case.

This is similar to #96.

Could it be that functions that generate a 'model':

a. Warn and rename the existing .model columns to something else? Or
b. Is this clash detected at the start of the function call and a suitable error thrown?

Here's an example of my code:

library(dplyr)
library(fable)
library(feasts)

tsibbledata::aus_retail %>%
    filter(`Series ID` == 'A3349606J') %>% 
    model(STL(Turnover)) %>% 
    components() %>% 
    model(ETS(season_adjust)) %>% 
    forecast(h = 12)

The errors:

Error: Failed to create output due to bad names.
* Choose another strategy with `names_repair`
Run `rlang::last_error()` to see where the error occurred.

█
├─<error/rlang_error>
│ Failed to create output due to bad names.
│ * Choose another strategy with `names_repair`
└─<error/vctrs_error_names_must_be_unique>
  Names must be unique.
Backtrace:
  1. dplyr::filter(., `Series ID` == "A3349606J")
  1. fabletools::model(., STL(Turnover))
  1. generics::components(.)
  1. fabletools::model(., ETS(season_adjust))
  9. fabletools::forecast(., h = 12)
 12. tidyr:::pivot_longer.data.frame(...)
 13. tidyr::pivot_longer_spec(...)
 19. vctrs::vec_cbind(...)
 21. vctrs:::validate_unique(names = names, arg = arg)
 22. vctrs:::stop_names_must_be_unique(names, arg)
 23. vctrs:::stop_names(...)
 24. vctrs:::stop_vctrs(class = c(class, "vctrs_error_names"), ...)
Run `rlang::last_trace()` to see the full context.

Reproduce the supplied aus_retail pipeline from model(), components(), model(), and forecast() to confirm the duplicate .model failure. Trace how these entry points create and combine model columns, then define behavior for the clash so the example no longer produces non-unique names; the issue leaves warning/renaming versus an early error as open alternatives.