feat(cache): resolve remote cache configuration

[wan9chi]

Motivation

Each planned execution needs a resolved remote cache endpoint and access mode. Resolve these settings before execution while keeping cache controls out of task environments and cache fingerprints.

Add workspace remoteCache.url, task-level remoteCache: false, --remote-cache=off/read/read-write, and the VP_REMOTE_CACHE and VP_REMOTE_CACHE_URL environment variables. Flags override the current environment, command-specific overrides remain scoped, and the default is read with an endpoint or off without one. Disabling local caching also disables remote access.

Plan snapshots cover precedence, inheritance, override isolation, task exclusions, invalid settings, and Windows environment-name casing.

[github-actions]

fspy benchmark

linux

dynamic/launch             change  +0.16%  [ -8.42% ..  +8.30%]  overhead  +292.49%
dynamic/access             change  +0.01%  [ -5.44% ..  +4.48%]  overhead   +15.28%
dynamic/access-relative    change  +0.31%  [ -4.14% ..  +5.19%]  overhead   +61.15%
dynamic/access-contended   change  +2.15%  [ -8.06% .. +16.11%]  overhead   +20.92%
static/launch              change  -0.07%  [ -6.68% ..  +7.55%]  overhead  +699.21%
static/access              change  -0.53%  [-12.78% ..  +5.39%]  overhead  +810.36%
static/access-relative     change  +0.41%  [ -1.56% ..  +3.22%]  overhead +1352.31%
static/access-contended    change  -0.11%  [ -6.92% ..  +1.60%]  overhead +3114.80%

macos

dynamic/launch             change  -0.56%  [ -5.14% ..  +4.65%]  overhead  +224.38%
dynamic/access             change  +0.70%  [ -2.08% ..  +3.58%]  overhead    +3.56%
dynamic/access-relative    change  +1.63%  [ -2.69% ..  +5.79%]  overhead  +263.89%
dynamic/access-contended   change  +1.51%  [ -4.10% ..  +9.23%]  overhead    +2.00%

windows

dynamic/launch             change  +0.01%  [ -8.20% ..  +9.51%]  overhead   +24.09%
dynamic/access             change  +1.21%  [ -2.95% .. +23.14%]  overhead    +3.99%
dynamic/access-relative    change  +0.17%  [ -7.64% ..  +4.90%]  overhead    +1.55%
dynamic/access-contended   change  +0.33%  [ -3.23% ..  +8.09%]  overhead    +0.71%