Fix: Remove unnecessary API calls during tool execution and Handle execution errors better

[haxzie]

Note

Removes redundant connected-account lookups and consolidates tool execution with centralized before/after modifiers and improved API error-to-SDK error mapping.

• Core (tool execution):
  • Remove pre-execution connected account fetch and per-tool execution handlers; add executeComposioTool to call API and transform responses.
  • Centralize modifier application in execute() for both custom and Composio tools; route to customTools.executeCustomTool or executeComposioTool.
• Errors:
  • Add handleToolExecutionError to parse APIError and map codes (e.g., 1803) to specific errors like ComposioConnectedAccountNotFoundError.
  • Simplify ComposioToolExecutionError constructor and expand possible fixes.
• Tests:
  • Update test utilities to remove getConnectedAccountIdForTool spying and related setup.

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