Speed up import rlcompleter by deferring inspect and re

rlcompleter imports inspect and re at module scope, but neither is needed to import the module or to construct a Completer. Each is used in exactly one completion method:

• inspect: only in Completer._callable_postfix
• re: only in Completer.attr_matches

inspect in particular is a heavy import: it transitively pulls in dis, tokenize, and more. Because rlcompleter is imported during interactive startup (to set up tab completion via readline), this import cost is paid on every interactive session and every import rlcompleter, even though the completion methods may never run.

Linked PRs

• gh-156364

從 rlcompleter 模組以及 issue 中提到的 Completer._callable_postfix 和 Completer.attr_matches 進入點開始。驗證變更前後的匯入行為，並確認即使匯入 rlcompleter 不再為未使用的相依套件付出代價，補全行為仍然正確。