refactor(state): rename StateTooStale to StateRotten for clarity

[molon]

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[Copilot]

Pull request overview

This pull request refactors the codebase by renaming StateTooStale to StateRotten for improved clarity in describing the state of cached data that has exceeded both fresh and stale TTLs and must be refreshed.

• Renames the constant StateTooStale to StateRotten across all code, tests, and documentation
• Updates all comments, error messages, and test descriptions to use "rotten" terminology
• Maintains consistent behavior while improving code readability with more intuitive naming

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
types.go	Renamed StateTooStale constant to StateRotten and updated inline comment
error.go	Updated error message from "too stale" to "rotten" for consistency
entry_test.go	Renamed test cases and test data from "too stale" to "rotten" terminology
entry.go	Updated return statement to use StateRotten
client_test.go	Updated test names, assertions, and most comments to use "rotten" terminology; one inline comment needs update
client.go	Updated case statements and comments from "Too stale" to "Rotten"
README.md	Updated documentation diagrams and code examples to reflect new terminology
README_ZH.md	Updated Chinese documentation to reflect new terminology

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

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