refactor(sim): reuse PR33 link-budget helpers

[Komzpa]

Summary

This is the small reusable optimization slice from the stale #33 after the work was split along the discussion in #39 and #50.

The new review surface on top of #72 is intentionally narrow:

• estimate_path_loss() can take an explicit path-loss model= without mutating Config.MODEL, so scenario or analysis code can compare models without leaking global config state
• MeshPacket records the receiver IDs it already classified as CAD-detected or sensitivity-sensed while refreshing link budgets
• MeshNode.transmit() reuses those receiver-ID lists instead of scanning every node again for flags that were just computed

Stack context

GitHub shows the full stacked diff against master until the lower PRs merge. The dependency stack below this PR is #68, #69, #70, #73, #74, #75, #71, and #72. Those carry the map/terrain/clutter/RF/DCR/DTP pieces; this PR only adds the PR33 helper cleanup needed on top of that stack.

Why this shape

The useful part from #33 here was not the whole old branch. Maintainer feedback on #33 asked to separate optimizations from Burning Man-specific code, and #39/#50 asked for smaller reviewable PRs.

What is deliberately left out:

• lib/signal.py: Sync modem presets with current firmware #33 adds it, but the old branch does not import or call it from the simulator path, so reviving it here would add dead API surface without a caller
• burningManSim.py: kept out of this PR because it is scenario-specific and depends on the newer DCR/DTP/radio-policy stack; that belongs in the separate feat(sim): add Burning Man DCR/DTP scenario #78 scenario PR
• modem preset sync and other neutral cleanups from Sync modem presets with current firmware #33: those were already split into earlier focused PRs or are unrelated to this receiver-classification optimization

Validation

• MPLBACKEND=Agg .venv/bin/python -m unittest tests.test_phy tests.test_lora_mesh_cli tests.test_node tests.test_dtp tests.test_packet -v -> 58 tests OK
• git diff --check origin/pr/72..origin/pr/77
• GitHub unittest check is green

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 3f9a5afe9d

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 0a25ca3d8a

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".