TxPool: move validateBlobTx out of `global mutex` critical section

```
func (p *TxPool) validateBlobTxn
```
func seems doesn't use any `p` non-atomic fields. Unclear why it needs to be inside `p.mu.Lock()` section.

I guess: such heavy `validation of tx-object itself` - must be right after `rlp deserialization` - before insertion to `pool`.

And only `dynamic validation checks - which depend on current state of accs or pool - need to stay under p.mu.Lock()`. For example next need to stay `under p.my.Lock()`:
```
if !isLocal && (p.all.blobCount(txn.SenderID)+uint64(blobCount)) > p.cfg.BlobSlots {
```

I didn't bench it - so, i don't know "how much current validation affectiong txpool" - I just saw it in profiler

Start at TxPool.validateBlobTxn and trace its callers around p.mu.Lock(). Compare the validation that uses only the transaction object with dynamic checks such as p.all.blobCount(txn.SenderID), then inspect the surrounding TxPool flow. Done means object validation no longer runs in the global mutex section while state-dependent checks remain protected, with txpool behavior unchanged.

Written by the indexing model from the issue text.