Add transactional multi-channel scope focus

[Scaxlibur]

Summary

• add the portable scope.focus_configure_v2 contract, descriptor profile, operation spec, driver protocol, and Core-owned transaction
• add wavebench scope focus with repeated target channels, optional full time range, per-channel V/div, and --hide-others
• snapshot every profile analog channel plus protected time position, vertical range, position, and offset fields
• keep the requested view after success; restore the complete baseline and freshly verify it after any partial failure
• poison the session when restoration or verification is incomplete

Scope

Core remains hardware-neutral. Channel topology, numeric request guards, tolerances, and I/O budgets belong to each plugin descriptor profile. This PR does not add run-plan, TUI, HTTP MCP, autoscale, coupling, or input-termination behavior.

Validation

• 2103 passed, 1 skipped, 131 subtests passed
• full Ruff check passed
• git diff --check passed
• CLI help and capability explain output verified

Stack and PR #3

This PR is stacked on #15 so review shows only the focus changes. After #15 merges, its base can move to master.

Together, #15 and this PR satisfy the observation-view goals of #3: channel display control, multi-channel focus, timebase adjustment, per-channel vertical scale, and hiding other analog channels, with current capability and recovery semantics.