feat(cva): support internal variants prefixed with _

[joe-bell]

Variant names starting with _ are now internal: still declarable in
variants, settable via defaultVariants, and matchable in
compoundVariants, but hidden from the component's props type and
from getSchema (both its return type and runtime object). Hiding is
type-level only, so an untyped caller can still resolve one directly.

This is a breaking change for any config that already used a
_-prefixed variant name as a public prop; those variants disappear
from prop types and getSchema results, though their runtime class
resolution is unaffected. Documented in variants.mdx, api-reference.mdx,
and flagged in whats-new.mdx.

Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01ALpEtdErxKFkdm3jhvSjmS

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	cva	d5eb7a9	Commit Preview URL Branch Preview URL	Jul 12 2026, 06:54 PM

[joe-bell]

Unsure about this approach, would an internalVariants key be better 🤔

[github-actions]

Benchmarks

Comparing this PR's local benchmark run against the latest published npm versions.

Aim for higher ops/s. Treat deltas within ±5% as noise.

class-variance-authority

Task	This PR	0.7.1	Δ
cva (runtime) component call with defaults	1,138,165 ops/s ±0.12%	1,111,138 ops/s ±0.29%	+2.4%
cva (runtime) component call with props	178,275 ops/s ±0.27%	190,144 ops/s ±0.33%	🔴 -6.2%
cx (runtime) class join	12,262,745 ops/s ±0.37%	12,636,414 ops/s ±1.72%	-3.0%
cva (static) component definition	24,983,440 ops/s ±0.22%	22,957,015 ops/s ±0.60%	🟢 +8.8%
compose (static + runtime) define, join and call	944,171 ops/s ±0.39%	935,170 ops/s ±0.91%	+1.0%

cva

Task	This PR	1.0.0-beta.6 (beta)	Δ
cva (runtime) component call with defaults	1,110,925 ops/s ±0.18%	1,147,788 ops/s ±0.63%	-3.2%
cva (runtime) component call with props	176,792 ops/s ±0.17%	176,395 ops/s ±0.54%	+0.2%
cx (runtime) class join	11,153,386 ops/s ±0.11%	8,983,262 ops/s ±0.52%	🟢 +24.2%
cva (static) component definition	4,051,796 ops/s ±0.80%	3,834,469 ops/s ±1.59%	🟢 +5.7%
composes property (static + runtime) define, join and call	449,454 ops/s ±0.23%	454,774 ops/s ±0.37%	-1.2%

_{Commit e1d355b · Node v24.18.0 · linux x64 · 2026-07-12T18:54:24.986Z}

_{These benchmarks ran in CI on this PR's code. The comment checks that the report looks valid before posting it, but it cannot guarantee the numbers are correct. If you see a large change, re-run the benchmarks locally before treating it as a real improvement or regression.}