chore(jdbc): suppress expected compiler warnings (#248)

## Why

The build runs `-Xlint:all`, so every run reports expected warnings. Two
tests exercise the deprecated Unicode stream API on purpose, the
vendored xerial tree uses deprecated JDK methods, and the parameter
metadata view triggers a `this` escape that it cannot actually cause.
The noise makes a new warning hard to see.

## What changed

- Suppress `deprecation` on the two tests that exercise the deprecated
Unicode stream methods.
- Suppress the deprecation detail and javac's summary note for the
`libsql-conformance` test compile, which includes the vendored xerial
sources.
- Suppress `this-escape` on the `LibsqlPreparedStatement` constructor
and document why the view is safe.

## Scope

No behavior change. The deprecated calls stay in the tests, and the
vendored tree stays untouched. Only the compiler diagnostics are
suppressed, and only where the warning is expected.

## Tradeoffs

`-XDsuppressNotes` is an internal javac option. It is scoped to the
conformance test compile, and the build pins the JDK.

## Blast Radius

Compiler diagnostics only. The driver and its tests are unchanged, and
the `libsql-conformance` main sources keep the full lint set.

## Verification

- `clean verify`: 2,006 tests, 0 failures, 7 skipped, `BUILD SUCCESS`.
- `libsql-jdbc` clean test: 1,510 tests, 0 failures, with no
`deprecated` or `this-escape` warning.
- Conformance test compile: no deprecation detail and no summary note.
- `spotless:check` passes.

The JDK's `sun.misc.Unsafe` warning from ByteBuddy is unrelated and
remains.

Author: magnusp

libsql-conformance/pom.xml

@@ -163,6 +163,23 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <!-- The vendored xerial tests use deprecated JDBC API on purpose.
+                     Suppress the deprecation detail and javac's summary note for the test compile. -->
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>default-testCompile</id>
+                        <configuration>
+                            <compilerArgs combine.children="append">
+                                <arg>-Xlint:-deprecation</arg>
+                                <arg>-XDsuppressNotes</arg>
+                            </compilerArgs>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>

libsql-jdbc/src/main/java/com/github/magnusp/libsql/jdbc/LibsqlPreparedStatement.java

@@ -52,6 +52,9 @@ public class LibsqlPreparedStatement extends LibsqlStatement implements Prepared
     // Sequential list indexed by JDBC parameter position; no map or boxing overhead.
     private final List<Value> parameters = new ArrayList<>();
 
+    // ParameterMetaDataView only stores this reference and calls checkClosed() after construction,
+    // so no subclass method can run against a half-built statement.
+    @SuppressWarnings("this-escape")
     public LibsqlPreparedStatement(LibsqlConnection connection, String sql) {
         super(connection);
         this.sql = sql;

libsql-jdbc/src/test/java/com/github/magnusp/libsql/jdbc/LibsqlPreparedStatementTest.java

@@ -409,6 +409,8 @@ void unsetParametersBindNullArguments() throws SQLException {
                 .containsExactly(Value.of(7L), Value.ofNull());
     }
 
+    // The deprecated Unicode stream setter is part of the local-conversion contract.
+    @SuppressWarnings("deprecation")
     @Test
     void streamSettersBindLocalConversions() throws SQLException {
         RecordingConnection connection = new RecordingConnection(NO_ROWS);

libsql-jdbc/src/test/java/com/github/magnusp/libsql/jdbc/LibsqlResultSetTest.java

@@ -457,6 +457,8 @@ void findColumnRejectsNullLabel() {
                 .hasMessageContaining("null");
     }
 
+    // The deprecated Unicode stream getters are part of the unsupported-method contract.
+    @SuppressWarnings("deprecation")
     @Test
     void everyUnsupportedMethodThrowsSqlFeatureNotSupportedException() throws SQLException {
         LibsqlResultSet rs = resultSet(new Value.Integer(1));