[Feature Request] Consider exporting MCP method constants so consumers don't have to reimplement

[tjhop]

Is your feature request related to a problem? Please describe.
Currently, the library has a list of MCP method names as constants:

go-sdk/mcp/protocol.go

Lines 1330 to 1357 in 67bd3f2

	const (
	methodCallTool = "tools/call"
	notificationCancelled = "notifications/cancelled"
	methodComplete = "completion/complete"
	methodCreateMessage = "sampling/createMessage"
	methodElicit = "elicitation/create"
	notificationElicitationComplete = "notifications/elicitation/complete"
	methodGetPrompt = "prompts/get"
	methodInitialize = "initialize"
	notificationInitialized = "notifications/initialized"
	methodListPrompts = "prompts/list"
	methodListResourceTemplates = "resources/templates/list"
	methodListResources = "resources/list"
	methodListRoots = "roots/list"
	methodListTools = "tools/list"
	notificationLoggingMessage = "notifications/message"
	methodPing = "ping"
	notificationProgress = "notifications/progress"
	notificationPromptListChanged = "notifications/prompts/list_changed"
	methodReadResource = "resources/read"
	notificationResourceListChanged = "notifications/resources/list_changed"
	notificationResourceUpdated = "notifications/resources/updated"
	notificationRootsListChanged = "notifications/roots/list_changed"
	methodSetLevel = "logging/setLevel"
	methodSubscribe = "resources/subscribe"
	notificationToolListChanged = "notifications/tools/list_changed"
	methodUnsubscribe = "resources/unsubscribe"
	)

It would be helpful to consumers of this library if these constants could be exported so they don't need to be re-implemented.

For a concrete example, I have a telemetry middleware that handles metrics/logging for various things. In order to properly handle telemetry for, eg: tool calls vs resource calls, I use a type switch on the MCP method to do the correct things for the correct methods. Because the library doesn't export the MCP method constants, I need to reimplement the method names that I care about instrumenting:
https://github.com/tjhop/prometheus-mcp-server/blob/main/pkg/mcp/middleware.go#L12-L39

It'd be nice to defer to upstream/official constants from the library, if possible.

Describe the solution you'd like
Export the MCP method name constants so library users can use them directly.

Describe alternatives you've considered
I've already implemented a workaround, as shown. Other ideas are welcome.

Additional context

[maciej-kisiel]

Personally, I'm not sure this brings enough value to increase the (already big) public API surface of the SDK.