fix: support tools with arguments named "self"

[andreitava-uip]

Due to the way StructuredTool is implemented, it will fail if the tool is supposed to take an argument named self, because of its special convention in Python, even if the function is perfectly valid. See issue. This is very relevant for MCP and IS tools, where the user has little control over the argument names.

As a fix on our side, we can extend StructuredTool and override the problematic _run() and _arun() methods, only renaming the conventional self param to an unconventional name, to reduce chances of collision.

Added tests that:

• validate the actual implementations to always match the langchain upstream, except for the argument renaming. this will allow us to quickly determine if there is a mismatch and resync the implementation.
• validate that the tool factory always produces our new BaseUiPathStructuredTool.