chore: upgrade docs build toolchain and fix RTD build

[magajh]

What this PR does:

Fixes a broken Read the Docs build caused by an outdated pinned Sphinx version, modernizes the documentation toolchain, and updates conf.py to be compatible with the upgraded dependencies.

Changes:

• Upgrades .readthedocs.yml to use ubuntu-24.04 and Python 3.12
• Unpins all documentation requirements, letting pip resolve the latest compatible versions
• Removes unnecessary internal Sphinx dependencies from requirements
• Updates html_sidebars in conf.py — sidebar-logo.html renamed to navbar-logo.html in sphinx-book-theme 1.x
• Removes unsupported logo_only and extra_navbar theme options from conf.py
• Upgrades requirements/pip-tools.txt (dev tooling only, no runtime impact)

Root cause of the broken build:

sphinx==4.2.0 depends on pkg_resources (from setuptools), which is no longer available by default in modern Python environments. Upgrading Sphinx removes this dependency entirely.