txnprovider/shutter: additional tests and fixes for pool cleanup and options handling + follow up - avoid using a 2nd copy and re-use signed copy

[taratorio]

cherry-pick #16505
cherry-pick #16554

---

closes #14287

adds tests in pool_test.go for:

• pool cleanup - verify both encrypted and decrypted txn pools get cleaned up
• blob txns are skipped from shutter pool - if accidentally ending up in the txn pool (matches nethermind)
• pool taking into account WithGasTarget and WithTxnIdsFilter options for ProvideTxns

fixes for discovered issues:

• we weren't updating the cleanup metrics for the encrypted txn pool (made it look like the pool isn't getting cleaned up and leaking mem)
• found a bug in EncryptedTxnSubmissionLess which is used to traverse the submissions tree
• we weren't calling txnParseCtx.ParseTransaction with correct input for hasEnvelope
• we weren't taking into account gas target and txn ids filter options
• we had incorrect logic for signing blob txns (there were no usages for it across the codebase before these new tests were added)
• added a error log in case the pool unexpectedly stopped due to some err and ProvideTxns was called - makes it much easier to see that the background goroutines are no longer operational
• simplified logic for MaxDecryptionKeysDelay (better protection for very long waits for unexpected future slot inputs)
• fixes an issue that caused our validators to crash a month ago:

[EROR] [07-08|16:59:33.000] background component error               err="decryption keys processor issue: decryption keys processing loop: unexpected item txn index lt next txn index: 38275 < 38276"

note: im making use of experimental (go1.24) synctest - it will be added as stable in go1.25