feat(types): Allow the Params property to be typed, instead of any - #11081

Similar to/Follow-up to #1061

Resubmission of #6807

Summary

Currently, it is not possible to have AxiosRequestConfig.params correctly typed—it will always be any. This PR changes that.

Linked issue

Closes #4954

Changes

• Makes AxiosRequestConfig.params generic, so it can be typed/the type be inferred

Checklist

• Tests added or updated (or N/A with reason)
• Docs/types updated if public API changed (index.d.ts and index.d.cts)
• No breaking changes (or called out explicitly above)
• The changes are not stale
• The PR has a reviewer
• The PR has no unaddressed feedback

Summary by cubic

Adds a params generic to axios request configs and propagates it across the public types for stronger typing and inference, with no runtime changes. Default request methods and AxiosPromise now preserve the request data and params types on response.config.

Description

• Summary of changes
  • Added P to AxiosRequestConfig<D = any, P = any> and propagated to RawAxiosRequestConfig, InternalAxiosRequestConfig, AxiosDefaults, CreateAxiosDefaults, AxiosResponse<T, D, H, P>, AxiosError<T, D, P>, CanceledError<T, D, P>, isCancel<T, D, P>(), isAxiosError<T, D, P>(), all request aliases and callable AxiosInstance, adapters, AxiosPromise<T, D, P>, and mergeConfig<D, P>() in both ESM (index.d.ts) and CJS (index.d.cts).
  • Introduced an internal AxiosResponseDefault to keep existing generic positions; defaulted request aliases now return AxiosResponse<T, D, {}, P> so response.config.data and response.config.params mirror the request types.
  • Made CustomParamsSerializer<P> and ParamsSerializerOptions<P> generic and tied to the request params type; withXSRFToken callback now receives InternalAxiosRequestConfig<D, P>.
• Reasoning
  • Type-safe query params and serializers, better inference in responses/errors/cancellation guards, and compatibility via P = any.
• Additional context
  • Usage: AxiosRequestConfig<MyData, MyParams> or method aliases with trailing P, e.g. axios.get<T, R, D, P>(...).

Docs

• Update TypeScript and API docs for AxiosRequestConfig<D, P>, generic CustomParamsSerializer<P>/ParamsSerializerOptions<P>, propagation to InternalAxiosRequestConfig, AxiosResponse, AxiosPromise<T, D, P>, AxiosError, CanceledError, isCancel, request aliases/callable instances, adapters, and mergeConfig<D, P>().
• Add a short example showing typed params, a serializer receiving P, and defaulted alias/AxiosPromise responses preserving response.config.data/params; note P = any default and unchanged generic order.

Testing

• Added/updated type-level tests (ESM/CJS) to verify:
  • params and serializers use P.
  • Propagation to InternalAxiosRequestConfig, AxiosResponse.config, AxiosError.config, and isCancel narrowing.
  • Method aliases, callable instances, AxiosPromise<T, D, P>, and mergeConfig preserve D and P.
  • Legacy untyped usage compiles; invalid param shapes error as expected.

Semantic version impact

Minor: additive typing changes with P = any default; no runtime changes.

^{Written for commit 5a0d082. Summary will update on new commits.}