fix(cache): treat a cache entry with an overflowing duration as corrupt

[wan9chi]

Motivation

Fixes #780. A cache entry stores the task's duration as seconds plus nanoseconds, and decoding it called Duration::new without checking them. Seconds near u64::MAX with nanoseconds that carry over panic there, and release builds abort on panic, so a single corrupt or malicious remote cache entry killed the whole vp run instead of being a cache miss.

Changes

• Remove the hand-written DurationSchema and use wincode's built-in Duration schema. The adapter dates from the bincode migration (refactor: migrate from bincode to wincode #334), when wincode 0.5 had no Duration support. wincode 0.6's schema has the same encoding (u64 seconds, then u32 nanoseconds) and returns a decode error on overflow. The on-disk and remote formats don't change, so the cache schema version stays the same.
• Such an entry now fails to decode like any other corrupt remote value: it's a cache miss with remote cache value is corrupt as its reason.

🤖 Generated with Claude Code

[github-actions]

fspy benchmark

linux

dynamic/launch             change  -0.16%  [ -6.12% ..  +5.31%]  overhead  +295.41%
dynamic/access             change  +0.00%  [ -1.50% ..  +1.05%]  overhead   +14.60%
dynamic/access-relative    change  -0.32%  [ -1.19% ..  +0.76%]  overhead   +59.18%
dynamic/access-contended   change  +0.27%  [ -3.05% ..  +5.93%]  overhead   +17.46%
static/launch              change  -0.48%  [ -5.52% ..  +5.97%]  overhead  +750.21%
static/access              change  +0.16%  [ -2.32% ..  +1.26%]  overhead  +807.46%
static/access-relative     change  +0.09%  [ -2.29% ..  +1.37%]  overhead +1373.91%
static/access-contended    change  +0.03%  [ -1.36% ..  +2.10%]  overhead +3145.10%

macos

dynamic/launch             change  +0.46%  [ -7.02% .. +10.16%]  overhead  +221.76%
dynamic/access             change  +0.00%  [-11.06% .. +53.53%]  overhead    +1.30%
dynamic/access-relative    change  +0.76%  [-18.66% .. +51.04%]  overhead  +268.98%
dynamic/access-contended   change  -0.01%  [-58.74% .. +63.58%]  overhead    -0.78%

windows

dynamic/launch             change  -0.04%  [ -1.58% ..  +1.09%]  overhead   +25.61%
dynamic/access             change  +0.19%  [ -0.58% ..  +0.78%]  overhead    +1.16%
dynamic/access-relative    change  +0.18%  [ -1.08% ..  +1.30%]  overhead    +1.12%
dynamic/access-contended   change  +0.30%  [ -5.31% .. +12.87%]  overhead    +1.10%