refactor(typing): annotate self-returning methods with Self

[ThanasisMattas]

No description provided.

[alexanderankin]

we still support python 3.10, please change it back to typing_extensions and try to reduce the number of false test negatives so that i can focus on the other test failures - i think some are legitimate, and im not sure if they're specific to your branch.

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.26%. Comparing base (be4c857) to head (7fa3ac5).

Files with missing lines	Patch %	Lines
core/testcontainers/core/generic.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1008      +/-   ##
==========================================
- Coverage   83.29%   83.26%   -0.03%     
==========================================
  Files          16       16              
  Lines        1754     1757       +3     
  Branches      193      193              
==========================================
+ Hits         1461     1463       +2     
- Misses        236      237       +1     
  Partials       57       57              

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[Tranquility2]

I rebased this branch onto main and added a fix-up commit so that Self is imported from typing_extensions (the project still supports Python 3.10, where typing.Self doesn't exist).
The original commits broke every 3.10 CI job; with this fix, all 3.10 core tests now pass.

The remaining red jobs on this PR are pre-existing issues unrelated to the Self refactor, which I've split out into focused PRs:

• fix(k3s): use with_tmpfs_mount to avoid duplicate tmpfs kwarg #1034 — fix(k3s): use with_tmpfs_mount to avoid duplicate tmpfs kwarg
• test(milvus): cast exposed_port to str for substring assert #1035 — test(milvus): cast exposed_port to str for substring assert
• chore(ci): skip scylla module tests on Python 3.14 #1036 — ci: skip scylla module tests on Python 3.14
• test(rabbitmq): declare exchange and queue as durable #1037 — test(rabbitmq): declare exchange and queue as durable

Once those land, this PR should go fully green after a rebase.