[DRAFT] Replace Conan with vcpkg

[Twisol]

• Tickets addressed: N/A
• Review: By commit
• Merge strategy: Merge (no squash)

Description

This PR replaces the Conan-based build and dependency orchestration with a simpler vcpkg solution. This has the following intended benefits:

• Better interaction with GitHub Actions build caches;
• Shorter, fewer, and more memorable command-line invocations;
• Replacement of a layer "on top of" CMake (conan) with a layer "integrated into" CMake (vcpkg), reducing the number of distinct cognitive contexts that need to be juggled; and
• Removal of our dependence on an outdated version of Conan.

(There's also a deprecation warning removal in the first commit, which can be easily pulled out into a separate PR if desired.)

Verification

• TODO: Check that the updated GitHub Actions work.
  • https://github.com/lasp/basilisk/actions/runs/12217368793/job/34081548104?pr=356#step:9:105:

    Restored 59 package(s) from GitHub Actions Cache in 25 s. Use --debug to see more details.

• TODO: Check that the vcpkg caching works.

Documentation

• TODO: Update (and disseminate) build instructions using CMake (and its presets files) rather than Conan.

Future work

• The CMakeLists.txt files could still be refactored and simplified pretty drastically
• Investigate failure to cache the gtk2.0 package. One possible remedy is just not using GTK -- I threw together a Dockerfile that builds Basilisk unchanged with a collection of smaller packages instead of all of gtk2.0.
• Consider pre-building a Docker image with all of the system-level and Python-level dependencies, and have the CI use that image so that our CI time is just Basilisk build and test.

[Twisol]

Build cache :) from here:

Restored 59 package(s) from GitHub Actions Cache in 25 s. Use --debug to see more details.