feat(spec): omit versions from metadata views

[jdx]

Add SpecView::omit_version() for checked-in generated specs whose release automation manages versions separately. The base derived spec remains versioned, so runtime --version behavior is unchanged; only the cold metadata view omits it. A later version(...) override restores an explicit version.

Tests:

• cargo test -p usage-argv --all-features a_spec_view_applies_identity_and_sparse_effects_without_mutating_the_base
• cargo clippy -p usage-argv --all-features -- -D warnings

---

Note

Low Risk
Cold-path metadata only; parsing and version responses still use the base spec, with small API surface and test coverage.

Overview
Adds SpecView::omit_version() so cold-path metadata (KDL emission, help consumers) can drop the version string while the derived Spec still carries one for runtime --version.

The view tracks an omit_version flag: spec() and to_kdl() then emit no version instead of inheriting the base; calling version(...) clears omission and restores an explicit override. Tests cover base KDL still including version, omitted KDL without a version line, and omit_version then version ordering.

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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	4253	—
argh	6292	1.5x
clap	5893640	1385x
bpaf	21917948	5153x

                                              min       p01       p10    median
usage-rs: argv -> struct                      204       208       212       216  ns
argh: argv -> struct                          307       313       316       329  ns
clap: build tree + parse -> struct         479695    480817    483778    487853  ns
bpaf: build parser + parse -> struct      1581256   1581256   1595510   1602408  ns

usage: argv -> struct                             208 ns      0.21 µs
clap: build tree + parse -> struct             491078 ns    491.08 µs
clap: parse -> struct, tree reused              23189 ns     23.19 µs
clap: build tree only                          303662 ns    303.66 µs

_{5d9fb000af63 vs 0b137759b66b · measured on the runner, not pushed to the history.}