Bitarray

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* see [Bitarray 3 transition](bitarray3.rst)
* remove Python 2.7 support
* `.decode()` now returns iterator (equivalent to past `.iterdecode()`)
* `.search()` now returns iterator (equivalent to past `.itersearch()`)
* remove `.iterdecode()` and `.itersearch()`
* remove `util.rindex()`, use `.index(..., right=1)` instead,
deprecated since 2.9
* remove `util.make_endian()`, use `bitarray(..., endian=...)` instead,
deprecated since 2.9
* remove hackish support for `bitarray()` handling unpickling,
see detailed explaination in 207 - closes 206

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* add official Python 3.13 support
* update cibuildwheel to 2.21.3
* minor simplifications
* fix some typos

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* optimize initialization from strings by not constantly resizing buffer
* optimize `util.hex2ba()` and `util.base2ba()` by avoiding unnecessary
copies
* optimize `util.base2ba()` and `util.ba2base()` for `n=16` (hexadecimal)

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* avoid buffer being unnecessarily initialized with 0s in several
functions of the `bitarray.util` module
* fix `.count()` type hint in pyi-file
* improve testing

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* deprecate support for Python 2 - Python 2.7 support will be removed
in bitarray version 3.0,
see [roadmap](https://github.com/ilanschnell/bitarray#roadmap)
* `bitarray(n)` for integer initializer `n` will always return a bitarray
of length `n` with all items initialized to `0`, see 212
* allow sub-bitarray in `.count()`, 212
* add `util.ones()`
* `.find()` and `.index()`: add keyword argument `right` for rightmost index
* `.itersearch()`: add start and stop argument, and keyword
argument `right` (for descending order - starting with rightmost match)
* deprecate `util.rindex()` (will be removed in 3.0 release),
use `.index(..., right=True)` instead
* deprecate `util.make_endian()` (will be removed in 3.0 release),
use `bitarray(..., endian=...)` instead

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* speedup unaligned copies by always using word shifts (in combination
with builtin byte swap 64 when available) when bit-endianness and
machine byte-order are opposite
* add `HAVE_BUILTIN_BSWAP64` to header
* avoid misaligned pointers when casting to `(uint64_t *)`
* add tests