all: remove deprecated uses of math.rand (#26710)

This PR is a (superior) alternative to https://github.com/ethereum/go-ethereum/pull/26708, it handles deprecation, primarily two specific cases. 

`rand.Seed` is typically used in two ways
- `rand.Seed(time.Now().UnixNano())` -- we seed it, just to be sure to get some random, and not always get the same thing on every run. This is not needed, with global seeding, so those are just removed. 
- `rand.Seed(1)` this is typically done to ensure we have a stable test. If we rely on this, we need to fix up the tests to use a deterministic prng-source. A few occurrences like this has been replaced with a proper custom source. 

`rand.Read` has been replaced by `crypto/rand`.`Read` in this PR.

core/txpool/txpool_test.go

@@ -18,6 +18,7 @@ package txpool
 
 import (
 	"crypto/ecdsa"
+	crand "crypto/rand"
 	"errors"
 	"fmt"
 	"math/big"
@@ -92,7 +93,7 @@ func pricedTransaction(nonce uint64, gaslimit uint64, gasprice *big.Int, key *ec
 
 func pricedDataTransaction(nonce uint64, gaslimit uint64, gasprice *big.Int, key *ecdsa.PrivateKey, bytes uint64) *types.Transaction {
 	data := make([]byte, bytes)
-	rand.Read(data)
+	crand.Read(data)
 
 	tx, _ := types.SignTx(types.NewTransaction(nonce, common.Address{}, big.NewInt(0), gaslimit, gasprice, data), types.HomesteadSigner{}, key)
 	return tx