docs: DOC-640: Add local development guide for Deephaven libraries

[margaretkennedy]

Add comprehensive guide for building Java/Groovy projects with Deephaven dependencies, covering Gradle/Maven setup, common dependencies by use case, and local unit testing with ExecutionContext. Include cross-reference from Python docs.

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Python
Groovy

[Copilot]

Pull request overview

Adds a new “Local development with Deephaven libraries” guide to the Groovy docs (with a lightweight cross-reference page in the Python docs) and exposes both via their respective sidebars. This is intended to help users set up external Java/Groovy projects that depend on Deephaven artifacts, and to document a unit-testing pattern using ExecutionContext.

Changes:

• Add Groovy guide covering Gradle/Maven setup, “common dependencies by use case”, and unit testing notes.
• Add a Python stub page that links users to the Groovy guide for Java/Groovy-focused setup.
• Update both Groovy and Python sidebars to include the new “Local development” entry.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
docs/python/sidebar.json	Adds “Local development” to the Python how-to sidebar.
docs/python/how-to-guides/local-development.md	Adds a short Python page that links to the Groovy guide.
docs/groovy/sidebar.json	Adds “Local development” to the Groovy how-to sidebar.
docs/groovy/how-to-guides/local-development.md	Adds the full local development guide (Gradle/Maven + testing guidance).

Comments suppressed due to low confidence (1)

docs/groovy/how-to-guides/local-development.md:66

• The “Date/time utilities” entry references deephaven-FishUtil, but there is no FishUtil module in this repo. Update this row to the current artifact that actually contains Deephaven date/time utilities (the io.deephaven.time.* classes are in engine/time).

| Read/write Parquet files               | `deephaven-extensions-parquet-table`             |
| Configuration utilities                | `deephaven-Configuration`                        |
| Date/time utilities                    | `deephaven-FishUtil`                             |
| Logging                                | `deephaven-log-factory`                          |

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (2)

docs/groovy/how-to-guides/local-development.md:130

• The unit test example imports TestExecutionContext, which lives in the deephaven-engine-test-utils artifact (not in the main runtime dependencies). Add a note and dependency example (e.g., testImplementation io.deephaven:deephaven-engine-test-utils:<version>) so the snippet compiles for readers.

Use JUnit with an `ExecutionContext` to test table operations:

```java skip-test
import io.deephaven.engine.context.ExecutionContext;
import io.deephaven.engine.context.TestExecutionContext;
import io.deephaven.engine.table.Table;
import io.deephaven.util.SafeCloseable;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.*;

public class MyTableUtilsTest {

    private static ExecutionContext executionContext;
    private static SafeCloseable executionContextCloseable;

    @BeforeAll
    public static void setUp() {
        executionContext = TestExecutionContext.createForUnitTests();
        executionContextCloseable = executionContext.open();
    }

docs/groovy/how-to-guides/local-development.md:160

• The "Reading test data" snippet uses CsvTools and ParquetTools, which require adding the CSV/Parquet extension artifacts (deephaven-extensions-csv, deephaven-extensions-parquet-table). Add a brief note or dependency examples here so readers don't hit ClassNotFound errors when copying the snippet.

```java skip-test
import io.deephaven.csv.CsvTools;
import io.deephaven.parquet.table.ParquetTools;

import java.nio.file.Paths;

// Read CSV from test resources
Table csvTable = CsvTools.readCsv(getClass().getResourceAsStream("/test-data.csv"));

// Read Parquet from test resources
String parquetPath = Paths.get(getClass().getResource("/test-data.parquet").toURI()).toString();
Table parquetTable = ParquetTools.readTable(parquetPath);

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