Add nettools

[isbm]

Nettools are various networking tools to detect changes, such as default route, routing table, hostname etc.

[Copilot]

Pull request overview

Adds a new nettools sensor crate to Omnitrace for polling hostname and routing-table state and emitting structured change events via the existing callback hub.

Changes:

• Introduces nettools crate with NetTools sensor, backends, and NetToolsEvent/mask types.
• Adds demo binaries for hostname, routes, and default-route monitoring plus README docs.
• Adds async unit tests validating emitted events using deterministic sequence backends.

Reviewed changes

Copilot reviewed 7 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/callbacks.rs	Minor formatting adjustments in CallbackHub implementation.
nettools/src/lib.rs	Implements NetTools sensor, live backends (hostname + route polling), and change detection logic.
nettools/src/events.rs	Adds event and mask definitions for nettools.
nettools/src/nettools_ut.rs	Adds async unit tests for hostname/route/default-route events.
nettools/src/bin/nettools-hostchange.rs	Demo binary emitting hostname change events.
nettools/src/bin/nettools-routes.rs	Demo binary emitting route add/remove/change events.
nettools/src/bin/nettools-default-route.rs	Demo binary emitting default-route add/remove/change events.
nettools/src/bin/README.md	Usage docs for demo binaries.
nettools/README.md	Crate-level overview and example commands.
nettools/Cargo.toml	Declares the new crate and its bins/dependencies.
Cargo.toml	Adds nettools to workspace members.
Cargo.lock	Adds lockfile entries for the new crate.

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