Make spilling hash builder better report reserved memory

[sopel39]

Description

- reserve memory before creating a LookupSource
- yield if unspilled pages cannot fit memory immediately

Additional context and related issues

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## General
* Improve spilling reliability for join queries. ({issue}`25976`)

Fixes #25976

[Copilot]

Pull Request Overview

This PR enhances the HashBuilderOperator to better handle reserved memory during lookup source creation and unspilling, and updates revocable memory after compaction. It also adds new tests to validate these memory-waiting behaviors under spill/no-spill scenarios.

• Reserve memory before building the lookup source in finishInput and finishLookupSourceUnspilling, and yield if reservation is pending.
• Update startMemoryRevoke to adjust the revocable memory context after compaction.
• Add DriverTestContext helper and new tests in TestHashJoinOperator to verify that the operator waits for memory when finishing input and unspilling.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
core/trino-main/src/main/java/io/trino/operator/join/HashBuilderOperator.java	Added pre-reservation of memory contexts in finishInput, unspill logic changes, and compaction update in startMemoryRevoke.
core/trino-main/src/test/java/io/trino/operator/join/TestHashJoinOperator.java	Introduced DriverTestContext helper and new tests to assert that HashBuilderOperator waits for memory under spill/unspill conditions.

Comments suppressed due to low confidence (2)

core/trino-main/src/main/java/io/trino/operator/join/HashBuilderOperator.java:513

• [nitpick] Add a comment explaining that finishInput should be retried once the pending memory reservation completes, so readers understand why we return early here.

if (!reserved.isDone()) {

core/trino-main/src/main/java/io/trino/operator/join/HashBuilderOperator.java:587

• [nitpick] The flag unspilledPagesAdded could be renamed to something like pagesUnspilled or unspillCompleted to more clearly reflect that it tracks whether pages have been transferred into the index.

if (!unspilledPagesAdded) {

[raunaqmorarka]

lgtm % test failures

[sopel39]

flakes due to #21078

[sopel39]

cc @osscm