feat(coverage): write LCOV after 'wippy test' when WIPPY_COVERAGE is set

[xepozz]

Depends on wippyai/go-lua#35
(the line-coverage collector, which itself stacks on go-lua#34). This PR calls
that collector's WriteCoverageLCOV/CoverageSummary, so it needs a go-lua
version that includes #35 to build. Please land the go-lua PRs first.

What

Writes an LCOV coverage tracefile after wippy test when WIPPY_COVERAGE is
set, so the native test suite can be run under line coverage.

How

After the test entrypoint finishes in runWithUseCase (right after
shutdown.Perform), it calls the go-lua coverage collector:

if lua.CoverageEnabled() {
    dumpCoverage()
}

dumpCoverage writes the LCOV file and prints an aggregate summary. It runs on
both the clean-exit path and before os.Exit(exitCode) on a failing run, so
coverage is captured even when tests fail (failing tests still execute code).

Configured via env:

• WIPPY_COVERAGE — enable (read by go-lua at init).
• WIPPY_COVERAGE_FILE — output path (default coverage.info).
• WIPPY_COVERAGE_FILTER — substring the chunk/source name must contain
  (default: all sources).

Usage

WIPPY_COVERAGE=1 WIPPY_COVERAGE_FILE=coverage.info WIPPY_COVERAGE_FILTER=@app \
  wippy test --host <cli_host>
# → writes coverage.info (LCOV) and prints: coverage: <hit>/<found> lines (<pct>%)

The resulting coverage.info is consumed as-is by genhtml, Codecov, and editor
coverage plugins.

Performance

No-op when WIPPY_COVERAGE is unset: lua.CoverageEnabled() short-circuits, so
normal runs are unaffected.

Scope of changes

One file — cmd/wippy/cmd/run.go: the lua import, the dumpCoverage helper,
and the guarded call after shutdown.Perform.

[Copilot]

Pull request overview

Adds optional Lua line-coverage export for the wippy CLI by writing an LCOV tracefile after the command run completes when coverage collection is enabled (via WIPPY_COVERAGE as interpreted by go-lua). This enables running the native test suite under line coverage and emitting a summary + LCOV output for downstream tooling.

Changes:

• Imports github.com/wippyai/go-lua and guards coverage export behind lua.CoverageEnabled().
• Adds a dumpCoverage helper to write an LCOV file and print a summary, configured via WIPPY_COVERAGE_FILE and WIPPY_COVERAGE_FILTER.
• Invokes coverage dumping after shutdown.Perform(...) and before any non-zero os.Exit(exitCode).

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