rpc: add method name length limit and configurable message size limit

[MatusKysel]

This PR introduces two important improvements to the RPC system:

1. Method Name Length Limit

• Adds a limit of 256 characters for RPC method names to prevent potential abuse
• Prevents large method names from leading to excessive response sizes
• Limit is enforced in:
  • handleCall for regular RPC method calls
  • handleSubscribe for subscription method calls
• Added tests in websocket_test.go to verify the length limit functionality

2. Configurable WebSocket Message Size Limit

• Adds support for configuring message size limits on both client and server sides
• Previously, server side used a fixed default limit while client side supported configurable limits
• Changes include:
  • Modified WebsocketHandler to accept a messageSizeLimit parameter
  • Added messageSizeLimit field to wsConfig struct
  • Updated server code to pass the message size limit through to WebSocket handler
  • Updated test cases to pass appropriate message size limits
  • Fixed linter errors in test files by providing proper int64 values

Both changes maintain backward compatibility:

• Method name length limit only affects new calls with names exceeding 256 characters
• Message size limit defaults to wsDefaultReadLimit when not specified

[Copilot]

Pull Request Overview

This PR introduces two improvements to the RPC system: enforcing a 256-character limit on RPC method names and enabling configurable WebSocket message size limits.

• Added validations in the RPC handler for both standard and subscription method calls to enforce the method name length limit.
• Modified the WebSocket handler and related configuration to accept a messageSizeLimit parameter, with corresponding test updates.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rpc/websocket_test.go	Updated WebsocketHandler invocations and added tests for method name length limit.
rpc/websocket.go	Modified WebsocketHandler signature and logic to use a configurable messageSizeLimit.
rpc/json.go	Defined maxMethodNameLength constant.
rpc/handler.go	Added method name length validation in handleCall and handleSubscribe.
rpc/client_test.go	Updated WebsocketHandler invocations to pass messageSizeLimit.
node/rpcstack.go	Updated WebsocketHandler instantiation to accept messageSizeLimit from config.
node/node.go	Forwarded WSMessageSizeLimit from node configuration.
node/config.go	Added WSMessageSizeLimit configuration field.
node/api.go	Propagated WSMessageSizeLimit in API setup.

[Copilot]

Pull Request Overview

This PR introduces two improvements to the RPC system: enforcing a 256‑character limit on RPC method names and making the WebSocket message size limit configurable.

• Adds checks in both regular calls and subscription requests for method name length limits.
• Propagates a new configurable messageSizeLimit parameter throughout the server, client tests, and node configurations.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rpc/websocket_test.go	Updates tests to pass an explicit messageSizeLimit parameter and adds tests for method name length limits.
rpc/websocket.go	Modifies the WebsocketHandler signature to accept and use messageSizeLimit.
rpc/json.go	Introduces a constant for maxMethodNameLength.
rpc/handler.go	Adds error responses for method/subscription name lengths exceeding the limit.
rpc/client_test.go	Updates WebsocketHandler invocations to include a messageSizeLimit parameter.
node/*	Passes the new messageSizeLimit from node configuration to the RPC stack.

[alex-10072]

similar PR in Go-Ethereum: https://github.com/ethereum/go-ethereum/pull/31711/files