feat(picker): prefer multi-specific keybinds over the source keybinds

[rynoV]

Description

When creating a multi picker, it is currently difficult to override the keys defined in the multi's sources.

For example, if I have a config like:

        files = {
          win = { input = { keys = {
            ['<M-g>'] = { 'do_something' },
          } } },
        },
        smart = {
          multi = {
            'buffers',
            'files'
          },
          win = { input = { keys = {
            ['<M-g>'] = { 'do_something_else' },
          } } },
        },

M-g will run do_something in both the files and smart pickers, but with this PR it will run do_something_else in the smart picker

Related Issue(s)

I didn't find any open issues