Unified link converters

[Evanthx]

Unified the Link Converter code - modelling what was done for Java and bringing into the other SDKs:
temporalio/sdk-java#3068

There are multiple encoding and decoding methods for links, all pretty close but not quite. That had me worried as it is easy for them to get out of sync. This PR merges those methods.

ConvertWorkflowLinkToNexusLink was experimental and unused, and has been removed. It emitted a workflow-event path (/history) that could not be decoded as a Link_Workflow. Use ConvertLinkWorkflowToNexusLink instead.

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Note

Medium Risk
Link URL shape affects interoperability; the deprecated ConvertWorkflowLinkToNexusLink now emits a different (correct) path, which could surprise any caller that depended on the old /history URLs.

Overview
Refactors temporalnexus link conversion so workflow event, workflow, Nexus operation, and activity variants share one linkType table with shared encode / decode (path templates, regex, proto type names) instead of four parallel URL builders and parsers.

ConvertWorkflowLinkToNexusLink is deprecated and now delegates to ConvertLinkWorkflowToNexusLink, fixing output that incorrectly used a workflow-event path (…/history) and could not round-trip as Link_Workflow. Per-type public APIs and CommonLinkToNexusLink / NexusLinkToCommonLink dispatch are unchanged in intent; workflow-event query handling is only reorganized.

Tests add coverage for the deprecated helper fix and a shared path-ID escaping round-trip across all link kinds.

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