[Bug]: Fix flaky EventHub publish test, prevent nil-client crash, and optimize S3 ReadDir memory overhead

[Manidwiptam]

🐛 Bug Overview

This report details two critical issues regarding runtime safety and resource optimization within the framework:

1. EventHub: A missing initialization guard in Publish allowed execution to proceed with a nil producer client, introducing structural flakiness. Concurrently, the associated failure test was unstable and explicitly skipped.
2. S3 File System: The ReadDir implementation relied on a wide prefix-only lookup, fetching metadata for all deeply nested objects. This behavior caused unnecessary memory allocation overhead in dense directory structures.

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🕹️ Steps to Reproduce

1. EventHub Uninitialized State Execution

Creating an EventHub client and attempting a write sequence without an explicit connection hook:

// Configuration is valid, but Connect() lifecycle step is omitted
client := eventhub.New(cfg) 
err := client.Publish(context.Background(), cfg.EventhubName, []byte("msg"))

[adityakrmishra]

i m taking over it

[Manidwiptam]

@adityakrmishra So, can I now fill out the Google form for GoFr T-shirt & stickers?
Although I actually fix the issue and give a pull request too.
So, you can check that out, and if it was working, then you can just merge it.

[adityakrmishra]

Whoa, wait, what?! 🤯 @Manidwiptam I am actually not a core maintainer at all—I'm just a community contributor exactly like you! I saw the issue was unassigned so I just went ahead and built a fix for it. We can leave it to the actual maintainers to review the PRs!

BUT wait... did you say GoFr T-shirts and stickers?! 👀

@coolwednesday is this true?! I had a successful PR merged in the past, and I just opened PR #3498 for this issue, plus another one for the metrics middleware. If there is actually a way to get contributor swag, that would be incredibly cool! Let me know if that's a real thing!

[Manidwiptam]

@adityakrmishra Ohhh I get it. I already, fixed the bug and give it for merging. If they accept and merged it, then I get the T-shirt and Stickers.
I just sees the bug, fixed and give it for merging.
And I raised the issue thus they can see the bugs, and merged my code.
If you perviously merge any thing in this repo then you also can get the sawgs. Just go to the bottom of the Readme of this repo and you get the T-shirt and Stickers Google Form juts fill it and you get the sawgs.