ST: Optimize CPU/memory use for OM1.0 Text CT/ST parsing (`st-storage` and `created-timestamp-zero-ingestion` features)

Proposal

As observed accidently on main and without any feature flag we use a lot of memory for CreatedTimestamp call for OM text. This is .due to deep coping of parser on every CreatedTimestamp, so technically per every series (!). This was a known naive implementation we decided to accept when iterating on this feature in https://github.com/prometheus/prometheus/pull/14356

This issue is to minimize that memory use. We already discussed this, but to put it here:

• We should see if we can reuse existing parser (not copy it).
• If we have to copy, copy once and reuse a second parser (e.g. reset it's positions).

IMPORTANT: This is only relevant to OpenMetrics 1.0. We designed OM 2 to not have that problem.

Acceptance Criteria

• The additional memory use per OM Text scrape with CT feature is minimal (~within +5% max)

Related to https://github.com/prometheus/prometheus/issues/14217

Start in model/textparse/openmetricsparse.go at the CreatedTimestamp path and review how the OpenMetrics 1.0 parser is copied for each series. Measure memory for an OM text scrape with the created-timestamp feature, then verify the change keeps additional use within the stated roughly 5% limit.