Function load by "source hoge.zsh" is not completion.

I’d like to ask you to add completion "function loaded by `source`".
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開いているファイルにある関数を補完されますが、
`source`や`.`によって読み込まれた関数は補完されません。
なので、`source`などで読み込んだ関数も補完できるようにしてほしいです。
(Issue立てるのは初めてなので、何か問題があれば教えてください)

Start by locating the completion logic that discovers functions from the currently open file, then trace how `source` and `.`-loaded functions are represented. Reproduce the missing completion with a sourced zsh file and verify that those functions become available without breaking completion for functions in the open file.

Written by the indexing model from the issue text.