refactor(mcp): call pkg/functions directly for create and delete tools

[sneharathod7]

Summary
This PR refactors the Model Context Protocol (MCP) server's create and delete tools to call the core pkg/functions library directly, migrating away from the subprocess shellout pattern (completing part of #3771).

To support seamless coordination with the patterns established in #3778, this PR utilizes a lazy closure provider to wire the fn.Client directly into the MCP Server structure, bypassing circular instantiation dependencies. A backward-compatible executor fallback is preserved for backward compatibility and to guarantee that existing mock unit tests remain green.

🛠️ What Changed
Lazy Client Provider Wiring

Extended pkg/mcp/Server to include a clientProvider func() *fn.Client field.
Exposed the functional option WithClientProvider to initialize it.
Configured the lazy provider closure in cmd/mcp.go to capture the initialized client and bypass the circular dependency between newClient and mcp.New.
Direct create Scaffolding

Refactored tools_create.go to invoke client.Init(...) directly when clientProvider is active.
Implemented a clean, platform-independent deriveNameAndPath helper to accurately resolve target directories.
Added custom template repository support by dynamically instantiating localized template registries if --repository is requested.
Direct delete Deletion

Refactored tools_delete.go to invoke client.Remove(...) directly when clientProvider is active.
Incorporated a robust namespace defaulting mechanism (getNamespace) that queries the client's configuration, active Kubernetes context via k8s.GetDefaultNamespace(), or falls back to "default", matching CLI behavior.
Integration Testing & green coverage

Created TestTool_Create_DirectClient in tools_create_test.go to verify end-to-end scaffolding inside temporary testing directories.
Created TestTool_Delete_DirectClient in tools_delete_test.go to verify path-based and name-based deletions using real client contexts.
Maintained all previous unit tests by retaining a safe fallback to s.executor if the clientProvider is nil.
🧪 Verification & Test Runs
All unit and integration tests compile, run, and pass with 100% success:

bash
go test -v ./pkg/mcp
text
=== RUN TestTool_Create_DirectClient
--- PASS: TestTool_Create_DirectClient (0.04s)
=== RUN TestTool_Delete_DirectClient
--- PASS: TestTool_Delete_DirectClient (0.04s)
PASS
ok knative.dev/func/pkg/mcp 0.605s
The entire project compiles flawlessly:

bash
go build -o func.exe ./cmd/func
(Exit code: 0)

🔒 Checklist
I have read and followed the Knative contribution guidelines.
All existing unit tests pass cleanly.
New integration tests added to cover create and delete direct library client paths.
Core CLI subcommands build perfectly.

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: sneharathod7
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[knative-prow]

Hi @sneharathod7. Thanks for your PR.

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