feature(picker): dynamic path truncation

[buztard]

Did you check the docs?

• I have read all the snacks.nvim docs

Is your feature request related to a problem? Please describe.

Currently it's only allowed to use an integer value for path truncation. It's IMO pretty hard to find a value that works well for small and large picker windows.

Describe the solution you'd like

It would be great to have user defined truncate functions. For example:

          formatters = {
            file = {
              truncate = function(path, picker)
                -- normalize go pkg paths and turn
                -- /home/buz/.gvm/pkgsets/go1.24.0/global/pkg/mod/go.opentelemetry.io/otel/[email protected]/tracer.go
                -- into go.opentelemetry.io/otel/[email protected]/tracer.go
                path = path:match("pkg/mod/(.+@.+)$") or path

                -- use 80% of the available window width
                local width = math.max(vim.api.nvim_win_get_width(picker.list.win.win) * 0.8, 40)
                return Snacks.picker.util.truncpath(path, width, { cwd = picker:cwd() })
              end,
            },
          },

Describe alternatives you've considered

Allowing a percentage value like truncate = 0.8 would be an improvement as well

Additional context

No response

[disrupted]

duplicate of #1400