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

从 rlcompleter 模块以及 issue 中提到的 Completer._callable_postfix 和 Completer.attr_matches 入口点开始。验证更改前后的导入行为，并确认即使导入 rlcompleter 不再为未使用的依赖项付出代价，补全行为仍然正确。