Investigate prebuild create vs claim build times in dogfood

## Description

In our dogfood environment, the “Write Coder on Coder” template has prebuilds enabled for certain presets. We recently introduced new metrics for prebuild creation time (building into the pool) and prebuild claim time https://github.com/coder/coder/pull/19503, and added them to our observability stack.

These metrics show that claim durations sometimes exceed creation by about 1–2 seconds. Because prebuilds maintain a ready-to-use pool to reduce workspace start time, claims should be consistently faster than creations.

We already use a Terraform `lifecycle` block with `ignore_changes` as recommended in the [docs](https://coder.com/docs/admin/templates/extending-templates/prebuilt-workspaces#preventing-resource-replacement), yet this pattern suggests Terraform may still be replacing or re-provisioning resources during claim, or the claim path is performing extra work.

For reference, see the attached screenshot comparing average build times for a prebuild creation versus a claim on the Falkenstein preset in our dogfood instance.

## Investigation scope

Investigate the source of the additional claim-path latency relative to the create path.

Inizia con la creazione dei prebuild e le metriche di claim nello stack di osservabilità, confrontando i dati di dogfood di Falkenstein e il blocco lifecycle di Terraform con ignore_changes descritto nella documentazione collegata. Traccia i percorsi di create e claim per identificare l’origine degli 1–2 secondi aggiuntivi; il lavoro è completo quando la latenza aggiuntiva di claim è spiegata e qualsiasi sostituzione o reprovisioning di Terraform è confermato o escluso.

Scritto dal modello di indicizzazione a partire dal testo della issue.