fix: relax WithLogHandler(nil)/WithLogger(nil) to no-op across engines

[robbyt]

Summary

Relaxes WithLogHandler(nil) and WithLogger(nil) across the three engines' compiler packages so they're a no-op instead of returning an error. This makes them behave the way the rest of the package already does post-#85/#99 — every other nil-handler path routes through helpers.SetupLogger, which inherits from slog.Default().

Before

func WithLogHandler(handler slog.Handler) FunctionalOption {
    return func(c *Compiler) error {
        if handler == nil {
            return fmt.Errorf("log handler cannot be nil")
        }
        // ...
    }
}

After

func WithLogHandler(handler slog.Handler) FunctionalOption {
    return func(c *Compiler) error {
        if handler == nil {
            return nil
        }
        // ...
    }
}

The "true no-op" detail (rather than "set field to nil") matters: WithLogHandler(real) followed by WithLogHandler(nil) now leaves the real handler in place, matching caller intuition.

Idiomatic precedent

• Stdlib slog.NewTextHandler(w, nil) accepts nil opts and falls back to defaults.
• OpenTelemetry's otelslog.WithLoggerProvider defaults to the global provider when the option is omitted.
• The broader functional-options pattern treats Option(nil) as semantically equivalent to not calling the option at all — the absence already produces the default.

Out of scope

The redundant if cfg.handler != nil guards in polyscript.go:251/262/273 and engines/{extism,risor,starlark}/new.go:72/85 exist solely to work around the now-removed nil-rejection. They become harmless once this lands. Cleanup is tracked under #112 and depends on this PR.

Files changed

• engines/{extism,risor,starlark}/compiler/options.go — relaxed both options + godoc
• engines/{extism,risor,starlark}/compiler/options_test.go — flipped "errors on nil" → "no-op on nil + prior state preserved"
• engines/{risor,starlark}/compiler/compiler_test.go — same flip for the higher-level "Option error handling" subtest
• fmt import dropped from risor and starlark compiler/options.go (no longer used; extism keeps it)

Test plan

• go test -race -count=1 ./... — green
• go vet ./... — clean
• 8 updated tests assert no-op semantics + state preservation regression guard
• CI on the PR

Closes #111

https://claude.ai/code/session_01C61VEAmjxSnX5Xhbab8NvL

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Generated by Claude Code

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull request overview

This PR standardizes nil-logger/nil-handler behavior across the Extism, Risor, and Starlark compiler functional options so WithLogHandler(nil) / WithLogger(nil) become true no-ops (instead of returning errors), aligning compiler configuration with the rest of the logging setup that already falls back via helpers.SetupLogger.

Changes:

• Relax WithLogHandler(nil) and WithLogger(nil) in all three engine compiler option packages to return nil (no-op) rather than an error.
• Update/replace unit tests to assert no-op semantics and “prior state preserved” behavior for nil options.
• Update higher-level compiler option handling tests to expect nil options to succeed.

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
engines/starlark/compiler/options.go	Make WithLogHandler(nil) / WithLogger(nil) no-ops; update doc comments.
engines/starlark/compiler/options_test.go	Adjust option tests to assert no-op + state preservation.
engines/starlark/compiler/compiler_test.go	Update option-handling test to expect nil options to succeed.
engines/risor/compiler/options.go	Make WithLogHandler(nil) / WithLogger(nil) no-ops; update doc comments.
engines/risor/compiler/options_test.go	Adjust option tests to assert no-op + state preservation.
engines/risor/compiler/compiler_test.go	Update option-handling test to expect nil options to succeed.
engines/extism/compiler/options.go	Make WithLogHandler(nil) / WithLogger(nil) no-ops; update doc comments.
engines/extism/compiler/options_test.go	Adjust option tests to assert no-op + state preservation (multiple suites).

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