Backport of commits & various new fixes/features

[njroussel]

This PR backports some commits that were on master but were reverted before rebasing on the nanobind_v2 branch. They are all edge cases that were wrong in the C++ API, none of them were related to the Python API.

This PR also includes various features and fixes:

• Tests for this drjit-core PR: https://github.com/mitsuba-renderer/drjit-core/pull/91
• Changes to the texture API such that it's numerical precision is better behaved
• New types in the bindings used by Mitsuba for polarization
• Fixes for recursive calls, that would previously recurse infinitely during tracing.
• Fixes to symbolic loops when using AD operations inside of them. This fix (commit: https://github.com/mitsuba-renderer/drjit/commit/fe2526627650045b7a34f98fc75474aeda701468) is particularly hacky and I'm open to better suggestions.
• Minor other stuff (the commit messages are explicit enough)

@rtabbara I've included your fixes in this PR too