feat: add mempool interfaces

[kocubinski]

Description

Ref: #13150
Followed by: #13262

I am proposing Select(...) instead of ReapMaxBytes(...) as in ADR-60, since the ProcessProposal steps can be simplified from

1. Reap one or more transactions from the priority queue and collect them into one of two buffers -- valid and invalid.
2. For transactions that DO NOT violate the nonce validation, they are included in the valid buffer.
3. For transactions that DO violate the nonce validation, they are included in the invalid buffer.
4. Continue this process until the desired number of valid transactions are reaped or until the mempool is empty.
5. Provide Tendermint the list of all transactions from the valid buffer.
6. Re-insert all transactions, from both buffers, back into app-side mempool.

to

1. Select valid transactions which do not violate nonce validation from the mempool up to maxBytes.
2. Provider Tendermint the list of transactions

---

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[codecov]

Codecov Report

Merging #13249 (fbaca0b) into main (c32493a) will increase coverage by 0.23%.
The diff coverage is 41.66%.

@@            Coverage Diff             @@
##             main   #13249      +/-   ##
==========================================
+ Coverage   54.78%   55.02%   +0.23%     
==========================================
  Files         660      653       -7     
  Lines       56914    55521    -1393     
==========================================
- Hits        31182    30549     -633     
+ Misses      23232    22519     -713     
+ Partials     2500     2453      -47     

Impacted Files	Coverage Δ
baseapp/abci.go	67.01% <ø> (ø)
types/context.go	88.81% <ø> (ø)
types/tx_msg.go	100.00% <ø> (ø)
x/auth/tx/builder.go	80.19% <0.00%> (-0.54%)	⬇️
baseapp/baseapp.go	77.12% <50.00%> (-0.82%)	⬇️
x/distribution/simulation/operations.go	80.64% <0.00%> (-9.68%)	⬇️
crypto/keys/internal/ecdsa/privkey.go	81.13% <0.00%> (-1.89%)	⬇️
simapp/simd/cmd/testnet.go
simapp/export.go
simapp/utils.go
... and 15 more

[tac0turtle]

LGTM

[alexanderbez]

Wish I had a chance to review this prior to merge. I really think this should not exist here.

IMO all mempool logic should live in a mempool subpackage in baseapp/mempool.

[alexanderbez]

@kocubinski please. undo these changes in #13262 :)