[PR #9407/e653b281 backport][3.11] Add __slots__ to stream classes

[patchback]

This is a backport of PR #9407 as merged into master (e653b28).

What do these changes do?

We use __slots__ almost everywhere else in the codebase, however __slots__ were not implemented in stream

related issue #4618 (comment)

Are there changes in behavior for the user?

no

Is it a substantial burden for the maintainers to support this?

no

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.81%. Comparing base (4c67472) to head (c32ebfc).
Report is 3 commits behind head on 3.11.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.11    #9408   +/-   ##
=======================================
  Coverage   97.81%   97.81%           
=======================================
  Files         108      108           
  Lines       35142    35144    +2     
  Branches     4194     4194           
=======================================
+ Hits        34373    34375    +2     
  Misses        573      573           
  Partials      196      196           

Flag	Coverage Δ
CI-GHA	97.68% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.37% <100.00%> (+<0.01%)	⬆️
OS-Windows	94.88% <100.00%> (+<0.01%)	⬆️
OS-macOS	97.07% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	96.93% <100.00%> (+<0.01%)	⬆️
Py-3.10.15	96.86% <100.00%> (+<0.01%)	⬆️
Py-3.11.10	96.95% <100.00%> (+<0.01%)	⬆️
Py-3.11.9	97.01% <100.00%> (+<0.01%)	⬆️
Py-3.12.6	97.41% <100.00%> (+<0.01%)	⬆️
Py-3.13.0-rc.3	97.39% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	96.84% <100.00%> (+<0.01%)	⬆️
Py-3.9.20	96.78% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.16	96.39% <100.00%> (+<0.01%)	⬆️
VM-macos	97.07% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	97.37% <100.00%> (+<0.01%)	⬆️
VM-windows	94.88% <100.00%> (+<0.01%)	⬆️

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[bdraco]

Looks like 3.11 has another set outside of init