Refactors the vendored knex instrumentation off the OpenTelemetry tracing
APIs onto Sentry's span APIs, mirroring the mongoose (#21481) and mysql2
(#21509) streamlines.

- Replace `tracer.startSpan` + manual `context.with`/`.then`/`.catch` with
  `startSpan`. `Runner.query` returns a real, already-executing Promise, so
  `startSpan` can safely await it and auto-end the span while keeping it active
  so the underlying `pg`/`mysql2` driver spans nest correctly.
- Preserve the build-time `contextSymbol` parent + require-parent-span behavior
  (only instrument queries that run within an existing trace).
- Bake the `auto.db.otel.knex` origin into the span attributes and drop the
  `spanStart` hook from `index.ts`.
- Drop the env-gated `OTEL_SEMCONV_STABILITY_OPT_IN` dual-emission; only the OLD
  semantic conventions (`db.system`, `db.statement`, ...) were ever emitted.
  Behavior change: the unsupported stable-semconv opt-in is no longer honored.
- Hardcode `requireParentSpan`/`maxQueryLength` (the integration only ever used
  the defaults), delete the now-dead `types.ts`/`constants.ts` and
  `otelExceptionFromKnexError`, drop OTel `recordException`, and remove the
  blanket `eslint-disable`.
- Extend the `pg` integration suite with a failing query to cover the error
  path (`status: internal_error`).