fix(openapi): replace repeated path parameters

[pacocartones]

Summary

• replace every occurrence of a repeated OpenAPI path parameter
• reuse the same encoded value for each occurrence
• add a regression covering repeated placeholders and reserved characters

The current single replacement leaves later occurrences such as /accounts/{id}/mirrors/{id} unresolved. Using replaceAll preserves the existing encoding behavior while substituting every occurrence.

Validation

• all 20 requestBuilder tests pass
• type checking, ESLint and Prettier pass