Fix vcpkg cache paths for Linux and macOS

[fdcastel]

Problem

The vcpkg cache paths in main.yml for Linux and macOS were set to build/Release/vcpkg_installed, but CMakePresets.json sets VCPKG_INSTALLED_DIR to build/vcpkg_installed (shared across all presets). This path mismatch meant the cache was saving/restoring the wrong directory, causing vcpkg to rebuild all ~60 packages from source on every run (~9 min).

Windows was already using the correct path (build/vcpkg_installed).

Additionally, pull-request.yml was missing vcpkg cache steps entirely for all three platforms.

Changes

1. Fixed Linux and macOS cache paths from build/Release/vcpkg_installed to build/vcpkg_installed in main.yml
2. Added missing vcpkg cache steps to pull-request.yml for all three platforms (Linux, Windows, macOS)
3. Bumped cache key version to v3 to invalidate stale entries

Timing measurements

"Configure CMake" step (where vcpkg install runs)

Platform	Before (broken cache)	After (cache hit)	Improvement
Linux	9m 40s	18s	-9m 22s (97%)
macOS	8m 22s	1m 53s	-6m 29s (78%)
Windows	19m 11s	42s	-18m 29s (96%)

Total job time

Platform	Before (broken cache)	After (cache hit)	Improvement
Linux	11m 47s	2m 14s	-9m 33s (81%)
macOS	9m 56s	4m 00s	-5m 56s (60%)
Windows	23m 19s	5m 07s	-18m 12s (78%)

Workflow runs

• Baseline (main, broken cache): https://github.com/fdcastel/fb-cpp/actions/runs/22879333936
• Cold cache (first run): https://github.com/fdcastel/fb-cpp/actions/runs/22921487352
• Warm cache (second run): https://github.com/fdcastel/fb-cpp/actions/runs/22922934856