[RSDK-11420] - Use conan for cpp-sdk dep

[seanavery]

Summary

Replace the viam-cpp-sdk bundled in Docker base images with Conan package management for both Jetson and Pi targets.

• Add conanfile.py pinning viam-cpp-sdk/0.20.1
• All builds (make build, make package) now go through Conan (conan install + conan build)
• Remove SDK source install from both Dockerfiles (Dockerfile.base, Dockerfile.base.bullseye)
• Remove SDK-only apt deps from Pi image (libboost-all-dev, libgrpc++-dev, libprotobuf-dev, etc.)
• AppImage packaging and release artifact format unchanged

CI Changes

• Bumped all ARM runners from buildjet-2vcpu to buildjet-8vcpu (SDK builds from source, OOMs on 2vcpu)
• Added actions/cache for .conan-home across build.yml, unit.yml, deploy.yml — first build is ~20min, cached builds are fast
• Merged conan-build.yml smoke check into build.yml and deleted the redundant workflow
• Unit tests now use make conan-test which chains install → build → test
• Cache keys are per-target (jetson/pi) to avoid GCC 10/11 cache conflicts

Bullseye (Pi) Linker Fix

The SDK libviam_rust_utils.a references POSIX AIO symbols (aio_read, aio_write, etc.) that live in librt on Debian Bullseye (glibc 2.31). On Jammy (glibc 2.34+) these are merged into libc. The SDK Conan package declares -lrt but places libviam_rust_utils.a last in link order, after -lrt is already discarded. Fixed with -Wl,--no-as-needed in CMakeLists.txt.

Base Images

New base images pushed to ghcr.io with SDK removed (image size ~70% smaller):

• viam-cpp-base-jetson:0.0.7
• viam-cpp-base-pi:0.0.7

Known Constraint

No Linux arm64 prebuilt binaries exist on viamconan for any viam-cpp-sdk version. The SDK conan-publish.yml has an arm64 runner in its matrix but packages are not appearing — likely silent CI failure. Every CI run builds the full SDK dep chain from source; actions/cache amortizes this after the first run.

Test Plan

• Jetson: make build → make package → ldd clean (no libviam deps) — Canon + CI
• Pi: make build → make package → ldd clean — Canon + CI
• Unit tests green in CI
• Lint green
• Build Latest green (both targets)
• Build and push new base images (0.0.7) with SDK removed
• CI green with new 0.0.7 base images
• Deploy Jetson AppImage to hardware, verify module starts and connects to CSI camera
• Deploy Pi AppImage to hardware, verify module starts and connects to CSI camera
• Follow up with SDK team on missing Linux arm64 prebuilt binaries in viamconan

[seanavery]

NOTE: need to upload new pi base image with ssl