fix: gsoc and pss checks

[martinconic]

The pt-pss check was failing intermittently with "500 Internal Server Error" or timeouts, even when messages were successfully delivered. This PR adds retry logic and decouples the send confirmation from the message receipt verification.

The pt-gsoc check was timing out under high load when sending many chunks in parallel. This PR introduces a configurable Chunks option, reduces the default parallel chunk count, and implements a smart retry mechanism that only re-broadcasts missing chunks.

PSS Check (pkg/check/pss)

Reliability: Added retry logic (5 attempts) to SendPSSMessage.
False Positive Fix: Modified the check to succeed if the PSS message is received by the listener, even if the SendPSSMessage call returns an error (e.g., timeout).
Configuration: Updated default PostageDepth to 22 to align with testnet configuration.
GSOC Check (pkg/check/gsoc)

Reliability: Implemented a retry mechanism that detects missing SOC updates after the initial run and re-broadcasts only the missing chunks.
Context Safety: Added ctx.Done() checks in the retry loop to ensure the check respects context cancellation immediately.
Configuration:
Added a Chunks option to control the number of parallel updates (default: 3).
Updated default PostageDepth to 22.
Added strict validation: Returns an error if Chunks is ≤ 0 (previously defaulted silently to 3).

[akrem-chabchoub]

Should add chunks field in checks and local config ?

[gacevicljubisa]

Any idea if this relates to the same issue?
#524

@nugaon, @martinconic ?

[martinconic]

Any idea if this relates to the same issue? #524

@nugaon, @martinconic ?

I am not sure about what that PR tries to solve, I was just trying to address the errors occurring when running these checks.