feat: Add model selector node

[schrothbn]

Summary

Adds a new node that selects one of the connected language models depending on customizable conditions.

To make that possible some adjustments needed to be made in the core:

• Support multiple connection definitions of the same type for sub node connections (including validating required and maxConnections)
• N8nLlmTracing now (optionally) keeps track of the parent run index to connect dependant runs correctly
• Adjusted filtering in the LogPanel to correctly associate runs between sub nodes of sub nodes.

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/AI-982/choosing-model-based-on-expression-having-a-fallback-model-when-a

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[cubic-dev-ai]

cubic found 5 issues across 14 files. Review them in cubic.dev

_{React with 👍 or 👎 to teach cubic. Tag @cubic-dev-ai to give specific feedback.}

[codecov]

Codecov Report

Attention: Patch coverage is 80.51948% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...s/@n8n/nodes-langchain/nodes/llms/N8nLlmTracing.ts	0.00%	7 Missing ⚠️
...angchain/nodes/ModelSelector/ModelSelector.node.ts	92.10%	3 Missing ⚠️
...gine/node-execution-context/supply-data-context.ts	0.00%	3 Missing ⚠️
...e/node-execution-context/node-execution-context.ts	0.00%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[OlegIvaniv]

Nice one! Seems to be mostly working as expected, there's just a couple of issues I noticed when traversing nodes from NDV:

1. Model selector icon looks too dark:
   
2. The connected models are rendering for both inputs, not just the connected one:
   

[OlegIvaniv]

Could we improve the type here? Something like:

{
			modelIndex: number;
			conditions: {
				options: {
					caseSensitive: boolean;
					leftValue: string;
					typeValidation: string;
					version: number;
				};
				conditions: Array<{
					id: string;
					leftValue: string;
					rightValue: string;
					operator: {
						type: string;
						operation: string;
						name: string;
					};
				}>;
				combinator: string;
			};
		}

[OlegIvaniv]

Does modelIndex really come as a string? On my instance I see it as number, so we might not even need to parseInt it.