refactor: convert local tail-recursive helpers to loops

[bobzhang]

Motivation

• Remove small local tail-recursive helpers and convert them to explicit loop state machines to avoid recursion and make control flow explicit.
• Keep the string/bytes regex translators aligned by applying the same pattern to both implementations.
• Simplify List::foldi by removing an inner recursive helper and using a direct loop over the list, index and accumulator.

Description

• Replaced the generic tail-recursive iter helper with a loop (n, init) state machine in bytes/internal/regex_engine/translate.mbt and string/internal/regex_engine/translate.mbt.
• Replaced the local recursive go helper in List::foldi with an explicit loop (self, 0, init) in list/list.mbt.
• These are control-flow refactors only and do not change external APIs or public interfaces.

Testing

• Ran moon info and moon fmt successfully to update/format package interfaces.
• Ran moon check successfully with no lint/diagnostic issues reported.
• Ran moon test which executed 6061 tests with 6061 passed and 0 failed.

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Codex Task

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[coveralls]

Pull Request Test Coverage Report for Build 3175

Details

• 9 of 9 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.001%) to 95.552%

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Totals
Change from base Build 3174:	-0.001%
Covered Lines:	14072
Relevant Lines:	14727

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💛 - Coveralls