Refactor: Only source ls-colors.zsh when fzftab module isn't loaded

[alberti42]

Motivation

fzf-tab sources lib/zsh-ls-colors/ls-colors.zsh unconditionally. However, when the aloxaf/fzftab module is present and successfully loaded, filename coloring is performed directly by zsh through the module, so sourcing ls-colors.zsh is redundant.

What this PR does

• Unsets FZF_TAB_MODULE_VERSION at init to avoid stale values influencing the logic.
• Attempts to load aloxaf/fzftab (and keeps the existing rebuild/version-check logic).
• Sources ls-colors.zsh only if the module is not available or fails to load.

Result

No behavior change for users without the module; less work at startup for users with a working aloxaf/fzftab module.