feat(logging): add WithHandlerMiddleware option to NewHandler

[reyortiz3]

Motivation

Consumers that need to wrap logging.NewHandler's returned handler with a cross-cutting concern (trace-context stamping, redaction, sampling, ...) currently do it as a separate reassignment after the call:

handler := logging.NewHandler(logging.WithFormat(logging.FormatText), logging.WithLevel(level))
handler = myTraceContextHandler(handler)

This adds a WithHandlerMiddleware option so that wrap can be expressed declaratively in the options list instead, without logging taking a dependency on OTel or anything else — it only knows about func(slog.Handler) slog.Handler.

Changes

• WithHandlerMiddleware(fn func(slog.Handler) slog.Handler) Option — appends fn to an ordered list; NewHandler folds them over the base handler before returning. Multiple middlewares apply in call order, so the last one wraps outermost and sees each record first (documented and tested).
• New(opts...) picks this up for free since it just forwards to NewHandler.

Verification

• task lint: 0 issues
• task test (full module, -race): all packages pass
• task license-check: passes
• New tests: TestNewHandler_WithHandlerMiddleware (wraps the handler, no-op with no middleware given, multiple middlewares apply in the documented order)

Scope

Only logging/logging.go and logging/logging_test.go.