feat(sigsafe): iterate process arguments and environment

[wan9chi]

Motivation

Low-level fspy code needs allocation-free access to the current process arguments and environment. On Linux, that access must also avoid libc so it remains suitable for injected and signal-sensitive code.

This adds a shared current() API that snapshots argument and environment bounds together. Linux obtains both ranges from one /proc/self/stat read and iterates their memory directly. macOS exposes direct thin iterators backed by _NSGetArgv and _NSGetEnviron, then builds the portable fat current() view only from those thin APIs.

The Unix preload ctor obtains one Current snapshot and passes current.envs() through Client::from_env to decode_payload_from_env. The payload helper retains its existing name while accepting the environment iterator explicitly, so payload initialization avoids std::env. Exec wrappers retain their existing environment inheritance and PATH behavior.

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	cargo/​atoi@​3.1.0

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[github-actions]

fspy benchmark

linux

dynamic/launch             change  +2.60%  [ -2.48% ..  +8.99%]  overhead   +51.23%
dynamic/access             change  +0.45%  [-13.39% ..  +9.25%]  overhead    +5.78%
dynamic/access-relative    change  -0.38%  [ -7.01% ..  +8.36%]  overhead   +51.56%
static/launch              change  +1.06%  [ -6.36% ..  +8.88%]  overhead  +156.53%
static/access              change  +1.17%  [ -4.23% .. +13.96%]  overhead  +721.29%
static/access-relative     change  +0.05%  [ -4.44% ..  +4.98%]  overhead +1039.80%

macos

dynamic/launch             change  -0.07%  [ -3.42% ..  +3.91%]  overhead  +230.41%
dynamic/access             change  -0.35%  [ -4.04% ..  +4.69%]  overhead    +6.57%
dynamic/access-relative    change  -0.11%  [ -1.64% ..  +2.55%]  overhead  +232.52%

windows

dynamic/launch             change  +0.22%  [ -1.94% ..  +1.64%]  overhead   +26.97%
dynamic/access             change  +0.00%  [ -0.73% ..  +1.12%]  overhead    +1.14%
dynamic/access-relative    change  +0.22%  [ -0.73% ..  +2.51%]  overhead    +1.67%