feat: raise TypeError when @cachier is applied to an instance method

[Borda]

Applying @cachier to an instance method silently produces wrong results because 'self' is excluded from the cache key, causing all instances to share a single cached value. This change raises TypeError at decoration time by default.

• Add allow_non_static_methods: bool = False to config.Params
• Add allow_non_static_methods parameter to cachier() decorator
• Guard fires in _cachier_decorator after core.set_func(); follows the existing mongo/redis/sql guard pattern
• @staticmethod is unaffected (self is not its first parameter)
• Opt out per-decorator: allow_non_static_methods=True
• Opt out globally: set_global_params(allow_non_static_methods=True)
• Declare func_is_method: bool = False in _BaseCore.init
• Update set_func docstring with the name-based heuristic and cls gap
• Remove unreachable assert max_age is not None dead code (x2)
• Fix test_config.py global state leak (stale_after=60 int pollution)
• Update all existing instance-method tests to use the opt-out flag

Resolves #170

[Copilot]

Pull request overview

Adds a safety guard to prevent accidental cross-instance cache sharing by default when @cachier is applied to instance methods (where the first parameter is named self), while providing explicit per-decorator and global opt-outs.

Changes:

• Introduces allow_non_static_methods (default False) in global Params and as an optional @cachier(...) argument; raises TypeError at decoration time for instance methods unless opted in.
• Tracks whether the decorated callable is an instance method via _BaseCore.func_is_method, based on a signature/name heuristic.
• Updates docs and tests to reflect the new default behavior, and fixes a global-state leak in tests/test_config.py.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/test_smoke.py	Adds smoke coverage for classmethod behavior and instance-method guard behavior.
tests/test_general.py	Updates method-decorated tests to opt in to non-static methods.
tests/test_config.py	Restores global params after deprecation-warning test to prevent state pollution.
tests/test_caching_regression.py	Updates regression scenario to opt in for instance method decoration.
tests/test_async_core.py	Updates async method tests to opt in and clarifies intent via comments.
tests/redis_tests/test_async_redis_core.py	Opts in for async redis instance-method tests.
tests/mongo_tests/test_async_mongo_core.py	Opts in for async mongo instance-method tests.
src/cachier/cores/base.py	Adds func_is_method flag and documents/implements name-based detection in set_func.
src/cachier/core.py	Adds allow_non_static_methods arg + decoration-time guard; removes unreachable asserts.
src/cachier/config.py	Adds allow_non_static_methods to Params and documents it as decoration-time.
README.rst	Documents the new default TypeError and the opt-in flag for instance methods.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.94%. Comparing base (5c4f121) to head (7b33fc3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #368   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          12       12           
  Lines        1731     1735    +4     
  Branches      216      218    +2     
=======================================
+ Hits         1730     1734    +4     
  Partials        1        1           

Flag	Coverage Δ
local	59.30% <100.00%> (+0.09%)	⬆️
mongodb	40.69% <66.66%> (+0.13%)	⬆️
postgres	43.40% <33.33%> (-0.05%)	⬇️
redis	46.80% <66.66%> (+0.12%)	⬆️
s3	42.47% <33.33%> (+0.01%)	⬆️

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Files with missing lines	Coverage Δ
src/cachier/config.py	100.00% <100.00%> (ø)
src/cachier/core.py	100.00% <100.00%> (ø)
src/cachier/cores/base.py	100.00% <100.00%> (ø)

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[shaypal5]

It's a good change. It's a good change!