Enforce the coverage level already achieved

[EONRaider]

Summary

Closes#79.

Coverage ran on every CI build and failed on nothing.
[tool.coverage.report] set only show_missing, so a drop was reported
and then ignored. The bar had already been cleared — 1441 statements,
3 missed, 99.79% — it just was not held.

What's included

• pyproject.toml — fail_under = 98 under [tool.coverage.report],
  with a comment recording what the current figure is and why the gate
  sits below it.
• CHANGELOG.md — entry under ## [Unreleased] → ### Development.

Why 98 and not 100

The only three uncovered statements are Packet.__repr__ and the
__eq__NotImplemented branch. Both are trivially coverable, so 100
was tempting — but a gate at 100 turns every legitimately unreachable
branch into a CI failure and invites # pragma: no cover scattered
through the source to keep it green. 98 leaves roughly 26 statements of
slack against 1441: enough for a defensive branch, far too little for
coverage to erode quietly.

95, the other value the issue floated, allows ~72 uncovered statements.
That is more slack than this suite has ever needed.

Verification

• uv run ruff check and uv run ruff format --check are clean
• uv run mypy is clean (strict)
• uv run pytest passes locally — 702 tests
• CHANGELOG.md has an entry under ## [Unreleased]

Checked in both directions, so the setting is demonstrably read and
enforced rather than silently ignored:

fail_under = 98 → Required test coverage of 98.0% reached.
Total coverage: 99.79% exit 0
fail_under = 100 → FAIL Required test coverage of 100.0% not reached.
Total coverage: 99.79% exit 1

Notes

No source or test changes — the coverage figure is unchanged, only
enforced. CI already invokes pytest --cov=netprotocols, so the gate
applies to the existing command with no workflow edit.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QJnVMNGwTRDktC4rkABtgt

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