feat: Enable concurrent microbatch execution

[wmjones]

Resolves #914

Description

Declares MicrobatchConcurrency adapter capability so dbt-core 1.9+ can execute microbatch incremental batches in parallel threads instead of sequentially.

This is a one-line addition to DatabricksAdapter._capabilities. dbt-core already handles all concurrency orchestration — temp table uniqueness (via model.batch.id suffix in make_temp_relation), non-overlapping REPLACE WHERE predicates per batch, and sequential execution of first/last batches. The adapter just needs to opt in.

Why Support.Full: Concurrency control happens at dbt-core's Python threading level, not Databricks SQL level. Every DBR version and SQL Warehouse that supports replace_where inherently supports concurrent batch execution.

OPTIMIZE note: Per-batch OPTIMIZE calls can conflict under concurrency when liquid_clustered_by, zorder, or auto_liquid_cluster is configured. Users with those configs can set DATABRICKS_SKIP_OPTIMIZE=true as a workaround. Plain Delta tables are unaffected.

Tested on: SQL Warehouse with Unity Catalog (30-batch microbatch model, --threads 4, all batches passed, concurrent execution confirmed, zero duplicates).

Prior art: dbt-snowflake added the same capability in dbt-snowflake#1259.

Checklist

• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt-databricks next" section.

[sd-db]

Hi @wmjones, we are doing a the release today for 1.11.5 and would not be possible to add a new feature in the same release (includes dbt-core pinning upgrade). Can you update the CHANGELOG.md to target 1.11.5 instead ? Thx again for the PR !!

P.S. I am stating integration test runs and will report if I see any issues.

[sd-db]

@wmjones It seem concurrency is opt-in by default. What this means is that anyone who is using microbatch-incremental models will have concurrent execution enabled by default. In dbt-databricks there is a well-established behaviour flag system that you can use to gate this feature behind a flag (it would be False by default). I would suggest doing that so it can ship safely in a patch, and then flip the default to true around 1.12 as we should have good data points by then on prod behaviour. See --> b819a878 for more details on how you might do this...