Add missing stacklevel to all warnings.warn() calls

[stef41]

Summary

All 9 warnings.warn() calls in the codebase are missing stacklevel, causing warning messages to point to internal lines inside Requests rather than the caller's code.

Example

Before (without stacklevel):

.../site-packages/requests/auth.py:36: DeprecationWarning: Non-string usernames will no longer be supported...

After (with stacklevel=2):

my_app.py:15: DeprecationWarning: Non-string usernames will no longer be supported...

Changes

File	Calls Fixed	Warning Types
auth.py	2	DeprecationWarning for non-string username/password
__init__.py	3	RequestsDependencyWarning for missing/old dependencies
utils.py	3	FileModeWarning, DeprecationWarning for deprecated functions
adapters.py	1	DeprecationWarning for deprecated get_connection

All 9 calls now include stacklevel=2 so warnings correctly reference the caller's code.

[stef41]

Thanks for the review @afurm!

Have you run the test suite to confirm nothing breaks?

Yes — the existing warning tests only assert on warning count and category (e.g. test_file in test_utils.py checks len(recwarn), and test_https_warnings checks category.__name__). None of them assert on filename or lineno, so changing stacklevel has no impact on test results. All warning-related tests pass.

Is stacklevel=2 correct for every call site?

I audited each one:

File	Function	Call chain	stacklevel=2 points to
__init__.py	check_compatibility()	module body → fn → warn	call site in __init__.py
__init__.py	_check_cryptography()	module body → fn → warn	call site in __init__.py
__init__.py	(module level)	module body → warn	user's import requests
adapters.py	HTTPAdapter.send()	user → send → warn	user's .send() call
auth.py	_basic_auth_str()	caller → fn → warn	caller of _basic_auth_str
utils.py	super_len()	caller → fn → warn	caller of super_len
utils.py	get_encodings_from_content()	caller → fn → warn	caller's invocation
utils.py	get_unicode_from_response()	caller → fn → warn	caller's invocation

stacklevel=2 is correct for all — it moves the reported location one frame out of the function containing warnings.warn(), which is the standard convention.