Add metadata support to callTool method (#289)

According to
https://modelcontextprotocol.io/specification/2025-06-18/basic/index#meta,
the _meta parameter should be passable when calling tools. While the
CallToolRequest class (in types.kt) currently includes _meta in its
definition, SDK users cannot actually input _meta when invoking the
callTool method.

This Pull Request adds a metadata parameter to the CallTool method and
includes functionality to convert various data formats without loss.

Additionally, to encourage the use of valid Key name formats as defined
by the protocol, validation for prefixes has been implemented.

---------

Co-authored-by: MAERYO <maeryo@hanwha.com>
Co-authored-by: devcrocod <devcrocod@gmail.com>

kotlin-sdk-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/integration/kotlin/AbstractToolIntegrationTest.kt

@@ -484,7 +484,7 @@ abstract class AbstractToolIntegrationTest : KotlinTestBase() {
                   "result" : 11.0,
                   "formattedResult" : "11,000",
                   "precision" : 3,
-                  "tags" : [ ]
+                  "tags" : ["test", "calculator", "integration"]
                 }
         """.trimIndent()