fix(derive): keep parsed fields live for lints

[jdx]

Generated command construction now takes a shared reference to every parsed field. This preserves intentional parse-only compatibility flags under deny(dead_code) without adding optimized runtime work.

A facade regression compiles an ignored flag under #[deny(dead_code)], and PLAN records the adopter requirement.

This PR description was generated by Codex.

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Note

Low Risk
Small derive codegen tweak plus a regression test; no change to parse semantics or security-sensitive paths.

Overview
Generated command construction now takes a shared reference to every parsed field so intentional parse-only compatibility flags no longer trip deny(dead_code).

The extra reads are expected to optimize away. A facade regression compiles an ignored flag under #[deny(dead_code)], and PLAN records the adopter requirement.

^{Reviewed by Cursor Bugbot for commit 04240b0. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[github-actions]

Instruction counts

Nothing was compared, and so nothing was gated. No series appears on both sides: either the base has no measurements recorded, or the two were measured on different runner classes, which are deliberately not comparable — counts shift between machine types by more than a real regression does.

New, nothing to compare against: markdown on bamboo-v2-ubuntu24.04-x64-30vcpu-24gb-rust1.97.1, startup on bamboo-v2-ubuntu24.04-x64-30vcpu-24gb-rust1.97.1

_{Only instruction counts gate. Wall clock is shown for context — on identical hardware it moves 4-20% run to run.}

_{Measured by tak — instruction-counted CLI benchmarks, stored in this repository's git notes.}

Shadow comparison

Parsing mise use -g node@20 against a shadow of mise's committed spec.
Reported, not gated: the shadow grows as the derive learns to express more, so
what to watch is the ratio rather than either column.

framework	instructions, cold parse	vs usage
usage	4355	—
argh	6292	1.4x
clap	5893640	1353x
bpaf	21917948	5032x

                                              min       p01       p10    median
usage-rs: argv -> struct                      196       199       203       209  ns
argh: argv -> struct                          283       288       294       303  ns
clap: build tree + parse -> struct         472668    474279    476382    482479  ns
bpaf: build parser + parse -> struct      1586268   1586268   1589490   1599909  ns

usage: argv -> struct                             218 ns      0.22 µs
clap: build tree + parse -> struct             488602 ns    488.60 µs
clap: parse -> struct, tree reused              23356 ns     23.36 µs
clap: build tree only                          301245 ns    301.25 µs

_{91537ccaf6be vs 2fdaff5f655c · measured on the runner, not pushed to the history.}