feat(py): remove legacy custom tools (#3508)

This PR is **part 1 of 3** splitting
https://github.com/ComposioHQ/composio/pull/3505 to make the removal of
the old 2025 custom tools easier to review. It carries the **Python**
slice.

- removes the legacy `composio.tools.custom_tool` registry path:
`core.models.custom_tools`, `ExecuteRequestFn`, the old fallback
execution wiring, the security tests, and the example
- preserves the 2026 tool-router APIs: `composio.experimental.tool()`,
`composio.experimental.Toolkit`, inline custom-tool execution,
preload/attach/use flows, and `session.custom_tools()`
- bumps the Python workspace and all provider packages `0.13.1` →
`0.14.0`

## Notes

- This slice is a byte-identical subset of #3505 — the three split
branches recombine to that PR's exact tree. See #3505 for the original
local verification logs (`uv run --frozen nox -s chk`, targeted pytest);
CI re-runs per PR.

python/examples/custom_tools.py

@@ -1,83 +0,0 @@
-import requests
-from pydantic import BaseModel, Field
-
-from composio import Composio
-from composio.types import ExecuteRequestFn
-
-composio = Composio()
-
-
-class AddTwoNumbersInput(BaseModel):
-    a: int = Field(
-        ...,
-        description="The first number to add",
-    )
-    b: int = Field(
-        ...,
-        description="The second number to add",
-    )
-
-
-@composio.tools.custom_tool
-def add_two_numbers(request: AddTwoNumbersInput) -> int:
-    """Add two numbers."""
-    return request.a + request.b
-
-
-class GetIssueInfoInput(BaseModel):
-    issue_number: int = Field(
-        ...,
-        description="The number of the issue to get information about",
-    )
-
-
-@composio.tools.custom_tool(toolkit="github")
-def get_issue_info(
-    request: GetIssueInfoInput,
-    execute_request: ExecuteRequestFn,
-    auth_credentials: dict,
-) -> dict:
-    """Get information about a GitHub issue."""
-    response = execute_request(
-        endpoint=f"/repos/composiohq/composio/issues/{request.issue_number}",
-        method="GET",
-        parameters=[
-            {
-                "name": "Accept",
-                "value": "application/vnd.github.v3+json",
-                "type": "header",
-            },
-            {
-                "name": "Authorization",
-                "value": f"Bearer {auth_credentials['access_token']}",
-                "type": "header",
-            },
-        ],
-    )
-    return {"data": response.data}
-
-
-@composio.tools.custom_tool(toolkit="github")
-def get_issue_info_direct(
-    request: GetIssueInfoInput,
-    execute_request: ExecuteRequestFn,
-    auth_credentials: dict,
-) -> dict:
-    """Get information about a GitHub issue."""
-    response = requests.get(
-        f"https://api.github.com/repos/composiohq/composio/issues/{request.issue_number}",
-        headers={
-            "Accept": "application/vnd.github.v3+json",
-            "Authorization": f"Bearer {auth_credentials['access_token']}",
-        },
-    )
-    return {"data": response.json()}
-
-
-response = composio.tools.execute(
-    user_id="default",
-    slug=get_issue_info.slug,
-    arguments={"issue_number": 1},
-)
-
-print(response)