feat: support ingestion API

[emranbm]

Send ingestion events (currently just Traces) in async batches. Best regards to the old implementation sample

[Copilot]

Pull Request Overview

This PR introduces asynchronous event ingestion for Trace events and implements an option pattern for customizing traces. Key changes include the addition of new option functions in pkg/langfuse/options.go, comprehensive tests for client behavior in pkg/langfuse/client_test.go, and a refactor that removes the legacy pkg/client files.

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/langfuse/options.go	Adds WithTags and WithSessionID options to customize trace objects.
pkg/langfuse/client.go & client_test.go	Implements async event sending and prompt template conversion with accompanying tests.
internal/observer/.go and internal/models/.go	Introduces and integrates the observer pattern and updated models for ingestion events.
pkg/client/*	Removes legacy client files in favor of the new implementation in pkg/langfuse.
go.mod	Updates module dependencies to support the new functionality.

Comments suppressed due to low confidence (1)

pkg/client/client.go:1

• [nitpick] The removal of the legacy 'client' package files appears intentional. Please ensure that all references to these files are updated accordingly.

package client