Merge epic/file-schema-v6 into main

[kyasbal]

TODO: Description will be added soon

[gemini-code-assist]

Code Review

This pull request introduces the new KHI file format v6, migrating the serialization and parsing architecture to Protobuf. It adds extensive coding standards, guidelines, and architecture documentation, while removing legacy HTTP client, history, and parser models. It also updates the Google Cloud API call options to retry transient unauthenticated errors and refactors log ingesters and timeline mappers to use the new v6 Builder and accumulators. The review feedback suggests minor optimizations to avoid unnecessary allocations in WithAttrs and NewFieldFilterNode when attributes or keys are empty, as well as removing a redundant context error check in the log ingester task.

[gemini-code-assist]

If keys is empty, we can return original directly. This avoids wrapping the node in a fieldFilterNode and allocating the ignored map unnecessarily.

Suggested change

	func NewFieldFilterNode(original Node, keys []string) Node {
	if original == nil {
	return nil
	}
	if original.Type() != MapNodeType {
	return original
	}
	func NewFieldFilterNode(original Node, keys []string) Node {
	if original == nil {
	return nil
	}
	if len(keys) == 0 || original.Type() != MapNodeType {
	return original
	}

References

1. When implementing a node wrapper or filter that only applies to a specific node type (such as MapNodeType), perform the type check in the constructor or factory function and return the original node directly if it is not of the target type, rather than wrapping it and checking the type inside individual methods.

[gemini-code-assist]

The check if err := ctx.Err(); err != nil is redundant because hasErr() already checks ctx.Err() != nil and returns early on line 104. We can safely remove this redundant check.

Suggested change

	if hasErr() {
	return
	}
	if err := ctx.Err(); err != nil {
	setErr(err)
	return
	}
	if hasErr() {
	return
	}