feat: full_refresh_build config with prebuilt in-place rebuild path

[Benjamin-Knight]

Adds a full_refresh_build model config offering a lower-disk full-refresh rebuild path. Builds on the indexes feature shipped in v1.10.1. Resolve #749

value	behaviour
heap_then_index	Default. Load as heap, swap, then build clustered design. Unchanged.
prebuilt	Drop old table → recreate empty with final clustered design (CCI or clustered index) → INSERT WITH (TABLOCK). No intermediate copy, no swap → ~1x peak disk instead of ~2x.

Behaviour

• Applies only under --full-refresh and on first builds; normal runs keep the configured refresh. Takes precedence over table_refresh_method: dml.
• Drops the table, so {{ this }} self-references must be guarded by {% if is_incremental() %}; the adapter detects an unguarded self-reference in the compiled SQL and fails before dropping anything.
• Trade-off: during a rebuild the target is empty/loading with no backup; a failure leaves an empty/partial table (recovery: rerun --full-refresh).
• Full refreshes mark the target with a dbt_full_refresh_incomplete extended property until they complete, so a later normal incremental over a failed refresh errors instead of appending onto stale data.

Performance: parallel index build vs. serial insert (edition matters)

prebuilt swaps the default's post-load CREATE INDEX for an INSERT WITH (TABLOCK) into the existing index:

• Enterprise: the post-load index build is parallel, so prebuilt (serial insert) can be slower on large tables — you pay build time for the disk win.
• Non-Enterprise (Standard/Web/Express): the index build was serial anyway (parallel index ops are Enterprise-only), so prebuilt costs little/no extra time and is the clearer win.

The ~1x peak-disk benefit holds on every edition; only the time cost is edition-dependent.

Testing

• tests/functional/adapter/mssql/test_full_refresh_build.py — 13 tests covering columnstore/rowstore/incremental/contract prebuilt paths, the self-reference guard, invalid-config-before-drop, and the incomplete-refresh marker.