Setting fifc_keybinding doesn't preserve tab default behavior

[jdanbrown]

Describe the bug

• By default, fifc triggers on tab, which shadows fish's default tab completion and pager
• Helpfully, fifc exposes fifc_keybinding so the user can pick a different keybinding, in case they don't want to override the default behavior of tab in fish
• But if I try e.g. set -U fifc_keybinding ctrl-x, then fifc triggers on both ctrl-x and tab, and I can't use tab to trigger fish's default tab completion — which is confusing and undesirable, because users should have a way to keep fish's default tab behavior
• https://github.com/gazorby/fifc/blob/a01650cd/conf.d/fifc.fish#L15

    for mode in default insert
        bind --mode $mode \t _fifc                 # <-- Bug
        bind --mode $mode $fifc_keybinding _fifc
    end

To Reproduce

1. set -U fifc_keybinding ctrl-x
2. Start a new shell
3. ls <tab>
4. I'd expect this to trigger the default fish tab completion, but instead it triggers fifc's tab completion

System (please complete the following information):

$ fish --version
fish, version 4.0.1
$ uname -a
Darwin Dans-MacBook-Pro.local 24.1.0 Darwin Kernel Version 24.1.0: Thu Oct 10 21:03:15 PDT 2024; root:xnu-11215.41.3~2/RELEASE_ARM64_T6000 arm64 arm Darwin