chore: Cleanup native tests

[pramodsatya]

Description

Cleans up tests from presto-native-tests.

Motivation and Context

implicitCastCharNToVarchar config is not toggled in any of the native-tests and should not be a parameter in the tests.
Helper methods used to test custom functions are only used in TestCustomFunctions and should not be a part of NativeTestUtils.
Builder pattern should be used to get the queryRunner used in tests and function NativeTestUtils.createNativeQueryRunner should not be overloaded with different arguments.

Impact

NA

== NO RELEASE NOTE ==

[sourcery-ai]

Reviewer's Guide

This PR streamlines the native test suite by removing the unused implicitCastCharNToVarchar toggle, consolidating query runner creation through a builder pattern, and moving custom-functions helpers into their dedicated test class.

File-Level Changes

Change	Details	Files
Pruned implicitCharNToVarchar toggle from native test utilities	Removed the boolean charNToVarcharImplicitCast parameter from createNativeQueryRunner Deleted overloaded createNativeQueryRunner methods and getCharNToVarcharImplicitCastForTest helper Eliminated char-to-varchar implicit cast setting in nativeHiveQueryRunnerBuilder usage	presto-native-tests/src/test/java/com/facebook/presto/nativetests/NativeTestsUtils.java
Refactored builder to drop implicitCastCharNToVarchar support	Removed implicitCastCharNToVarchar field and setter from HiveQueryRunnerBuilder Updated getExternalWorkerLauncher calls to remove cast toggle parameter	presto-native-execution/src/test/java/com/facebook/presto/nativeworker/PrestoNativeQueryRunnerUtils.java
Isolated custom-functions helpers into TestCustomFunctions	Moved getCustomFunctionsPluginDirectory and findPrestoRoot into TestCustomFunctions Replaced NativeTestsUtils.createNativeQueryRunner with nativeHiveQueryRunnerBuilder and setupNativeSidecarPlugin Added necessary imports and Optional usage for pluginDirectory	presto-native-tests/src/test/java/com/facebook/presto/nativetests/TestCustomFunctions.java
Simplified aggregation tests by removing conditional char-cast logic	Dropped implicitCastCharNToVarchar field and init parameter from AbstractTestAggregationsNative Replaced conditional branches with assertQueryFails for CHAR casts Updated TestAggregations and TestOptimizeMixedDistinctAggregations to match new init and createQueryRunner signatures	presto-native-tests/src/test/java/com/facebook/presto/nativetests/AbstractTestAggregationsNative.java presto-native-tests/src/test/java/com/facebook/presto/nativetests/TestAggregations.java presto-native-tests/src/test/java/com/facebook/presto/nativetests/TestOptimizeMixedDistinctAggregations.java

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[sourcery-ai]

Hey there - I've reviewed your changes and they look great!

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[aditi-pandit]

Lets leave the implicitCastCharNToVarchar flag. Since its used in Meta production and likely elsewhere it would be good to try in tests.

[pramodsatya]

Reverted this change.

[pramodsatya]

Could you please take another look @aditi-pandit? Thanks.