boost v1.86.0 (redux)

[h-vetinari]

Fix fall-out from #213

[conda-forge-webservices]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

[h-vetinari]

WTH man, conda-build looks seriously broken here.

Rendered as:
```yaml
package:
  name: libboost  <- this should be boost-split!
  version: 1.86.0

and then proceeds to pick up libboost's configuration for the global build (build.sh / bld.bat), which doesn't have the right requirements.

PS. Now raised as conda/conda-build#5459, this seems to be cosmetic-only though, not the reason for the failures.

[h-vetinari]

No idea where this is coming from

$SRC_DIR/tools/build/src/build/feature.jam:491: in feature.validate-value-string from module feature
error: "3.10" is not a known value of feature <python>
error: legal values:

[h-vetinari]

Looking through the release notes, the vendored b2 goes from 5.1.0 for 1.85 to 5.2.1 for 1.86, and the release notes for that only mention python once:

Allow some tools to be default initialized with using multiple times. The tools are asciidoctor, fop, gettext, pkg-config, python, sass, and saxonhe.

[h-vetinari]

Bah, overall boost didn't pick up all the numpy 2.0 fixes that happened in boost/python: boostorg/python#446 😑