Add throughputBucket support to Cosmos computation expressions

[Copilot]

Azure Cosmos DB throughput buckets can be set per request, but the library’s computation expressions did not expose that capability. This change adds throughputBucket to the CE surface so request-level bucket selection can be composed the same way as the existing request options.

• CE surface

  • Added throughputBucket custom operations to request-option-based builders:
    • create / createAndRead
    • replace / replaceAndRead
    • replaceConcurrenly / replaceConcurrenlyAndRead
    • upsert / upsertAndRead
    • upsertConcurrenly / upsertConcurrenlyAndRead
    • delete
    • read
    • readMany
    • patch / patchAndRead

• Request option wiring

  • Added a shared internal helper that sets the Cosmos SDK RequestOptions.ThroughputBucket value across the supported request option types.
  • Builders that lazily create request options (delete, read, readMany) now initialize options when throughputBucket is specified.

• Coverage

  • Added focused tests that verify each affected builder persists the configured throughput bucket onto its generated request options.

Example:

let operation =
    create<MyDocument> {
        item document
        partitionKey document.PartitionKey
        throughputBucket 3
    }