[completion] Simplify matcher-list syntax

Refactor using `+` instead of repeating the case insensitive pattern.

modules/completion/init.zsh

@@ -56,8 +56,7 @@ zstyle ':completion:*:warnings' format '%F{red}-- no matches found --%f'
 zstyle ':completion:*' format '%F{yellow}-- %d --%f'
 zstyle ':completion:*' group-name ''
 zstyle ':completion:*' verbose yes
-local case_insensitive='m:{a-zA-Z}={A-Za-z}'
-zstyle ':completion:*' matcher-list ${case_insensitive} "${case_insensitive} r:|?=**"
+zstyle ':completion:*' matcher-list 'm:{a-zA-Z}={A-Za-z}' '+r:|?=**'
 
 # directories
 zstyle ':completion:*:default' list-colors ${(s.:.)LS_COLORS}