[mday-io]

Description

This PR adds the query execution context provider and SQL comment transport.
PR #6174 adds automatic model context.

Why

Warehouse query history records SQLMesh's plan or run marker, but it cannot
connect each statement to the model evaluation reported by an execution
observer. Applications need to use one evaluation ID in both records.

How

Add an opt-in provider to engine adapters. It returns an immutable
QueryExecutionContext, which SQLMesh serializes as bounded, escaped version-one
JSON in a SQL comment. Keep the legacy marker first. Omit optional metadata on
ordinary provider or serialization failures and continue the query. Preserve
provider settings when adapters are cloned. Prevent provider settings from
leaking into cached DuckDB adapters or the default state adapter. Add a runnable
example that builds context from observer events.

Roll back adapter-owned transactions when a provider or driver raises a
BaseException, then propagate the original cancellation. This prevents a later
statement from reusing an abandoned transaction.

The connection flag enables context comments. It does not infer model context.
An application provider must supply that context.

Test Plan

• 61 serializer, transport, configuration, and Jupyter output tests passed.
• Cancellation tests cover adapter-owned and nested transactions, adapters
  without transactions, and driver cancellation with query context disabled.
  All 130 adjacent adapter and connection-pool tests passed.
• All 15 CLI init and DLT tests passed, including the two updated config
  expectations. These slow tests are outside make fast-test.
• make style passed.
• make fast-test passed all six phases. 2,983 passed and 13 skipped.
• make doc-test passed. 29 passed.
• A native DuckDB check compared Context.plan(), Context.apply(), and
  Context.run(). Observer, materialization, and audit IDs matched for six
  batches. Hashes and rows were unchanged. Default state SQL had no rich context.
• The runnable example and isolated enable-condition mutation check passed.
• Documentation links and navigation passed. The strict MkDocs build was
  unavailable because MkDocs is not installed locally.

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO

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