refactor: move outlier functions to semantically correct files/packages

[Copilot]

Four functions lived in files that didn't match their purpose. This moves each to its natural home with no logic changes.

Changes

• strutil/json_clone.go (new) — extracts DeepCloneJSON from strutil.go; JSON deep-clone has nothing to do with string utilities
• mcp/helpers.go (new) — extracts marshalToResponse, unmarshalParams, and callParamMethod from pagination.go; these are general-purpose MCP helpers consumed by connection_methods.go, not pagination-specific code
• server/middleware.go — moves withResponseLogging from http_helpers.go; it's an http.Handler decorator and belongs alongside WithOTELTracing, authMiddleware, WithSDKLogging, etc.
• mcpresult/mcpresult.go (new, replaces content_items.go + text_content.go) — consolidates two tiny single-function files into one; NormalizeContentItems and ExtractTextContent form a single logical unit

Finding 5 (AgentTagsSnapshot in mcp/connection_logging.go) is left as-is pending circular import analysis.

[Copilot]

Pull request overview

This PR refactors internal helpers by relocating a handful of “outlier” functions into files that better match their responsibilities, without changing behavior. The goal is to improve code organization and discoverability across strutil, mcp, server, and mcpresult.

Changes:

• Moved DeepCloneJSON out of strutil.go into a dedicated json_clone.go.
• Extracted MCP JSON-RPC helper functions from pagination.go into a new helpers.go, leaving pagination focused on paging logic.
• Consolidated MCP result parsing helpers (NormalizeContentItems, ExtractTextContent) into a single mcpresult.go, removing the prior tiny single-purpose files.

Show a summary per file

File	Description
internal/strutil/strutil.go	Removes DeepCloneJSON from the general string-utility file.
internal/strutil/json_clone.go	Adds DeepCloneJSON in a semantically focused file within strutil.
internal/mcp/pagination.go	Removes non-pagination MCP helpers; keeps pagination primitives and list helpers.
internal/mcp/helpers.go	Adds shared MCP helper functions for response marshalling and param unmarshalling.
internal/server/http_helpers.go	Removes withResponseLogging from HTTP helpers (keeps request-body logging utilities).
internal/server/middleware.go	Adds withResponseLogging alongside other HTTP middleware/wrappers.
internal/mcpresult/mcpresult.go	Hosts both NormalizeContentItems and ExtractTextContent in one cohesive file.
internal/mcpresult/content_items.go	Removed as part of consolidating MCP result helpers.

Copilot's findings

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• Files reviewed: 8/8 changed files
• Comments generated: 0