netvsp: tracing improvements for error triage (#2625)

[erfrimod]

Clean cherry-pick of #2625

Adding tracing spans to control-path operations in VF Manager to try and help answer two questions:

1. If a VF Manager operation like ManaDeviceRemoved fails to complete in a timely fashion, which 'await' call are we stuck in? It could be try_notify_guest_and_revoke_vtl0_vf(), shutdown_vtl2_device(), or update_vtl2_device_bind_state() and tracing spans will provide entry and exit opcodes.
2. If a VF Manager operation like ManaDeviceRemoved starts taking longer and missing SLAs, tracing spans can help us narrow down which call is taking up additional time.

• Improves NetVSP observability by adding structured tracing spans around VF Manager operations: VTL2 device startup/shutdown, VTL0 VF arrival/removal/revoke, endpoint disconnects, bind-state updates.
• Makes NetVSP device logging more actionable by adding instance_id and/or channel_idx to queue/channel errors: open/close/restore.
• Minor consistency improvements to error tracing. err => error and making that field the first element.
• Readability improvement to state transition logic in DataPathSwitchPending handler. Turning double-nested 'if' check into a 'match(a,b)'.
• Fixes to minor typos found in comments in net_mana and tracelimit..

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[Copilot]

Pull request overview

This PR enhances NetVSP observability and maintainability by adding structured tracing spans to VF (Virtual Function) Manager operations, improving error logging consistency, fixing minor typos, and refactoring state transition logic for better readability.

Changes:

• Adds tracing spans to critical VF Manager async operations (device startup/shutdown, VF arrival/removal/revoke, endpoint disconnects, bind state updates) to help diagnose timing issues and performance bottlenecks
• Enriches error logs with contextual identifiers (instance_id, channel_idx) and standardizes error field naming (err → error)
• Improves code readability through refactoring (double-nested if to match expression) and fixes typos in comments

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
vm/devices/net/netvsp/src/lib.rs	Removes unused imports, adds instance_id/channel_idx to error logs, standardizes error field naming, refactors state transition logic to match expression, fixes typo
vm/devices/net/net_mana/src/lib.rs	Corrects comment typos (capitalization and grammar)
support/tracelimit/src/lib.rs	Fixes spelling in documentation example
openhcl/underhill_core/src/emuplat/netvsp.rs	Adds Display trait for Vtl0Bus, instruments async operations with tracing spans, extracts helper method for bind state updates, improves variable naming clarity