refactor: modernize typedef to using alias in streams.h #35798

This PR modernizes legacy typedef declarations to using aliases in src/streams.h.

This is part of an ongoing effort to modernize the codebase to C++11/C++14/C++17 standards, following the C++ Core Guidelines which recommend using over typedef for readability and consistency.

This change does not alter any behavior.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35798.

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Reviews

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From the guidelines:

Trivial pull requests or pull requests that refactor the code with no clear benefits may be immediately closed by the maintainers to reduce unnecessary workload on reviewing.

This is a trivial refactor with no clear benefit, so I'd ask you to close this pull request and its 9 siblings again. If you are interested in contributing to the project, I would suggest that you start out with reviewing some of the many open pull requests.

If anything, squash into #35799.