feat(std-net): add bounded port scan

[larimonious]

Summary

• Adds bounded std/net.port_scan(host, ports, opts) for explicit TCP port arrays only.
• Reuses std/net target policy and TCP probe behavior so private/special destinations stay guarded.
• Keeps ping() ICMP-only with clearer ICMP-unavailable errors.
• Makes reachable(host, opts?) useful by default: probes ICMP plus TCP ports 80/443, and treats tcp_ports as additional explicit TCP ports.

Verification

• cargo fmt --check
• cargo test --test std_net_tests -- --nocapture
• cargo test
• cargo build --profile dev-release
• ./target/dev-release/ntnt docs --generate

[greptile-apps]

Greptile Summary

This PR expands std/net with bounded TCP scanning and richer reachability behavior. It changes:

• Adds port_scan(host, ports, opts) for explicit bounded TCP port arrays.
• Updates reachable() to probe ICMP plus default TCP ports 80 and 443, with caller-provided extra ports.
• Keeps ping() ICMP-only with clearer unavailable-backend errors.
• Adds docs, examples, typechecker coverage, and std/net tests for the new behavior.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

_{Reviews (9): Last reviewed commit: "test(std-net): allow closed reachable de..." | Re-trigger Greptile}

[Copilot]

Pull request overview

This PR extends std/net with a bounded TCP port_scan() over explicit port arrays, and updates ping() to perform real ICMP-backed pings (without TCP fallback), with corresponding typechecker, tests, docs, and examples updates.

Changes:

• Add std/net.port_scan(host, ports, opts?) with port-count and concurrency bounds plus target-policy enforcement.
• Replace std/net.ping() stub behavior with a system ping-backed ICMP implementation and structured result parsing.
• Update Rust integration tests, typechecker signatures, reference docs, and a new example to cover port_scan (and updated ping behavior).

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/type_checker_tests.rs	Adds port_scan to std/net signature acceptance/rejection typechecking coverage.
tests/std_net_tests.rs	Updates ping behavior test and adds deterministic local open/closed port_scan tests.
src/typechecker.rs	Registers the port_scan function signature in the std/net module signatures.
src/stdlib/net.rs	Implements port_scan, restores ICMP-backed ping, and adds parsing/helpers/options for both.
examples/std_net_port_scan.tnt	Adds an opt-in example demonstrating bounded port scanning.
docs/STDLIB_REFERENCE.md	Documents the new port_scan API in the generated stdlib reference.
docs/AI_AGENT_GUIDE.md	Updates std/net guide content and examples to include port_scan.
design-docs/dd-046-std-net.md	Updates the design doc status dashboard and acceptance checklist for PR3 port scan.