feat: support TA-Lib C 0.8.1(next release)

[mario4tier]

Rebased onto dev, and finished against the now-frozen TA-Lib C 0.8.1 surface.

TA-Lib C 0.8.1 becomes the minimum required version — against an older one the
build fails at compile time, which is the loudest way to say so.

What it adds

• 201 functions, up from 161: the 40 TA-Lib C has added since 0.7.1.
• MA_Type: HMA, DISABLED, DEFAULT, ZLEMA, RMA.
• set_unstable_period(): 'RMA', 'HA', 'RVI'.

Three defects found on the way

• The generators strip TA-Lib C's own streaming declarations by name. The verb
  list missed _Value and _Clone, which 0.8.1 declares for every function —
  403 stream accessors would have been parsed as batch functions. It now skips
  anything mentioning a TA_<FUNC>_Stream handle.
• defaults.get('matype', 0) never matches a prefixed parameter, so KDJ's
  slowk_matype / slowd_matype defaulted to SMA where the C table says RMA.
  func.KDJ and abstract.KDJ returned different numbers, with no error.
• SUPERTREND's integer output was about to be documented with the
  candlestick "values are -100, 0 or 100" wording. It is a +1/-1 trend direction.

Verification

Built against a 0.8.1 library: 81 tests pass. Re-running the generators
reproduces the committed _func.pxi and _stream.pxi byte for byte, so nothing
was hand-edited into a generated file.

Nine surfaces are checked to name the same 201 functions — the C abstract table,
__TA_FUNCTION_NAMES__, get_functions(), _ta_lib.pxd, _func.pxi,
_stream.pxi, both halves of _ta_lib.pyi, and abstract.pyi.

New tests, each shown to fail against the bug it covers:

• test_func_and_abstract_agree — the two public APIs must return identical
  values for all 201. Reverting the KDJ fix makes it fail.
• test_stubs_parse / test_stubs_cover_every_function — the .pyi files ship
  beside py.typed, and nothing else in the build reads them.
• MA_Type dispatch for HMA/ZLEMA/RMA, plus DISABLED and DEFAULT.
• RMA, HA and RVI added to the unstable-period cases.

Left for the release commit

talib/_ta_lib.c is untouched — it is refreshed at release time, together with
the version bump and the regenerated docs. An sdist built before that refresh
would carry the 161-function C file.

CI still triggers on master only, so this PR ran no checks; the verification
above is local.