Make tx pool mock public

[MetaB0y]

I am sure it can be useful for testing reth extensions (because it is useful for me).

Also, I don't see a serious reason for not making those mocks (and usually any mocks in general) public.

[mattsse]

reasonable

[codecov]

Codecov Report

Merging #4611 (fdcf966) into main (b156cb9) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

Files Changed	Coverage Δ
crates/transaction-pool/src/test_utils/mock.rs	56.15% <0.00%> (ø)

... and 7 files with indirect coverage changes

Flag	Coverage Δ
integration-tests	16.72% <0.00%> (+<0.01%)	⬆️
unit-tests	63.97% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
reth binary	30.85% <ø> (ø)
blockchain tree	83.58% <ø> (ø)
pipeline	90.53% <ø> (ø)
storage (db)	75.32% <ø> (ø)
trie	94.88% <ø> (ø)
txpool	49.14% <0.00%> (ø)
networking	77.20% <ø> (-0.07%)	⬇️
rpc	57.36% <ø> (-0.01%)	⬇️
consensus	63.40% <ø> (ø)
revm	31.56% <ø> (ø)
payload builder	6.12% <ø> (ø)
primitives	86.51% <ø> (-0.03%)	⬇️