feat(sqlserver): Part 7 — adapter_impl.rs match arms

[axellpadilla]

Part of dbt-labs#15714 (upstream feature request). Depends on #1. Independent of #4, #5, #6 (can run in parallel).

adapter_impl.rs has 44 Fabric occurrences across ~15 functions today; expect a comparable number of new SqlServer arms once the compiler enumerates them post-Part-1. Largest part by arm count, though most are 1-2 lines each (mirror Fabric or unimplemented!()).

Work items

• valid_incremental_strategies — likely direct copy of Fabric's &[Append, DeleteInsert, Merge, Microbatch]
• list_schemas_inner schema column name
• get_adbc_execute_options
• get_constraint_support, alter_table_add_columns, is_replaceable, truncate_relation, grants (grant_access_to, standardize_grants_dict), metadata_adapter
• unimplemented!() for anything SQL Server genuinely doesn't support (explicitly fine for an initial contribution per the guide)
• cargo build -p dbt-adapter repeatedly until clean

Full detail: dbt-sqlserver-v2-roadmap plan/02-implementation-steps.md §5.5 ("Adapter behavior match arms")

PRs against sqlserver-v2-port in this repo, use Closes #<this issue>.