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Feature request: a reverse counterpart to Str::wrap

Feature request: a reverse counterpart to Str::wrap: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). Str::wrap() lets you surround a value with a before / after string, which is handy. I keep running into the opposite need across projects and there's no clean…

The task

`Str::wrap()` lets you surround a value with a `before`/`after` string, which is handy. I keep running into the opposite need across projects and there's no clean helper for it.

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.