feat(summary): introduce QueryProfile (#1730)

Introduce `QueryProfile`, a new profile API that supersedes the now
deprecated `ProfiledPlan`. `QueryProfile` distinguishes between
unavailable metrics and metrics whose value is `0`. This avoids ambiguity in
profiling results and provides a more transparent representation of
available profile data.

The new profile API is exposed through `Optional<QueryProfile> queryProfile()`
on `ResultSummary`, providing a more idiomatic and null-safe way to access
profile information.

Execution time is now exposed as `java.time.Duration` instead of a raw
`long` value with an implicit unit.

As part of this update, `Plan plan()` is deprecated in favour of
`Optional<Plan> queryPlan()`, providing a more idiomatic and null-safe
way to access query plan information.