fix: classify malformed request params as invalid params

[jstar0]

Summary

Classify typed request deserialization failures as JSON-RPC Invalid Params
instead of Internal error.

Fixes #830.

Changes

• translate SerializationException from typed request decoding to -32602
• return a stable Invalid params message without serialization internals
• cover malformed initialize requests through session and Streamable HTTP paths

Scope and risk

The catch is limited to request parameter deserialization after the JSON-RPC
method has been resolved. Envelope parsing, unknown methods, handler failures,
and successful requests keep their existing behavior.

Verification

./gradlew :integration-test:jvmTest --tests 'io.modelcontextprotocol.kotlin.sdk.server.ServerSessionInitializeTest'
./gradlew :kotlin-sdk-server:jvmTest --tests 'io.modelcontextprotocol.kotlin.sdk.server.StreamableHttpServerTransportTest'
./gradlew :kotlin-sdk-core:jvmTest --tests 'io.modelcontextprotocol.kotlin.sdk.shared.ProtocolTest'
./gradlew ktlintCheck apiCheck