fix(abstract): stop relying on Cython resolving __NAME from class scope

[mario4tier]

Cython emits 58 warnings on every build of this repo, all one kind:

warning: talib/_abstract.pxi:35:4: Global name __PANDAS_SERIES matched from within
class scope in contradiction to Python 'class private name' rules. This may change
in a future release.

The Function class reads seven module globals whose leading double underscore
makes them mangling-eligible. Python's own rules say those references should
resolve to _Function__PANDAS_SERIES and raise NameError; Cython resolves them
to the module global instead, and warns that it may stop doing so. Dropping one
underscore makes the code mean what it already does.

renamed	__PANDAS_SERIES __PANDAS_DATAFRAME __POLARS_SERIES __POLARS_DATAFRAME __ARRAY_TYPES __INPUT_ARRAYS_TYPES __INPUT_PRICE_SERIES_DEFAULTS
untouched	__TA_FUNCTION_NAMES__ — trailing underscores put it outside the mangling rule, and it is public

tools/generate_stream.py referenced them too, so talib/_stream.pxi is
regenerated. Three hanging-indent blocks re-aligned by one column.

Cython warnings: 58 → 0. gcc: 0 before, 0 after.

Nothing else moves

• dir() of talib, talib._ta_lib, talib.abstract and talib.stream, plus
  Function.info / .parameters / .function_flags, diffed before and after:
  the entire difference is those seven names in talib._ta_lib.
• The generated _ta_lib.c, regenerated with the pinned Cython 3.2.8 and
  normalised for the rename, differs in 38 lines — all of them the interned
  string table: the packed identifier blob, its length index, the
  content-addressed __pyx_kp_b_* macro names, and the byte count
  (111563 → 111555). No function body, no ABI, no code path, so performance
  is identical by construction.
• 1697 tests pass; python-dev.py check green on all four steps, including
  "regenerating must change nothing" and the no-Cython sdist build.

The one thing that technically changes for an outside caller is that
talib._ta_lib.__PANDAS_SERIES no longer exists. It is dunder-prefixed, absent
from __all__ and undocumented — private by every convention — but it is a name
that existed before.

[mrjbq7]

👍