Move shell to use truncate_text (#6842)

Move shell to use the configurable `truncate_text`

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Co-authored-by: pakrym-oai <pakrym@openai.com>

codex-rs/core/src/context_manager/mod.rs

@@ -1,5 +1,4 @@
 mod history;
 mod normalize;
 
-pub(crate) use crate::truncate::truncate_with_line_bytes_budget;
 pub(crate) use history::ContextManager;