`LeaseOutput` is slow with postgres backend

[yyforyongyu]

Issue

SendCoins takes much longer to run with postgres as the db backend, and this itest failure has been shown multiple times,

harness_rpc.go:97: 
        	Error Trace:	/home/runner/work/lnd/lnd/lntest/rpc/harness_rpc.go:97
        	            				/home/runner/work/lnd/lnd/lntest/rpc/lnd.go:374
        	            				/home/runner/work/lnd/lnd/itest/lnd_taproot_test.go:129
        	            				/home/runner/work/lnd/lnd/itest/lnd_taproot_test.go:52
        	            				/home/runner/work/lnd/lnd/lntest/harness.go:385
        	            				/home/runner/work/lnd/lnd/itest/lnd_test.go:139
        	Error:      	Received unexpected error:
        	            	rpc error: code = DeadlineExceeded desc = context deadline exceeded
        	Messages:   	Alice: failed to call SendCoins

Observations

Turns out that when using postgres, leasing outputs take much longer, which is called here when crafting the tx for SendCoins.

• For kvdb backend, the leasing of 100 utxos takes about 1 second.
• For postgres backend, the leasing of 100 utxos takes about 40 seconds.

Steps to reproduce

Running with make itest icase=sign_psbt/fund_and_sign_psbt backend=btcd,

2024-06-04 03:37:30.353 [INF] RPCS: [sendcoins] addr=2MzusuQmFdFCBgtns6LjnCnQemeAhRftiku, amt=0 BTC, sat/kw=12500, min_confs=0, send_all=true
2024-06-04 03:37:30.353 [DBG] SWPR: [WithCoinSelectLock] entered the lock
2024-06-04 03:37:30.453 [DBG] SWPR: [WithCoinSelectLock] finished fetching UTXOs
2024-06-04 03:37:30.453 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: 65734f6883a0949f4588589fda166b9339bfb77081cf77dad1ee91b5dc78c000:0
...leasing 98 more...
2024-06-04 03:37:31.616 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: 2fb2947606ac7bf141ae364e8ea8d805344f56a319b679efa4380e6839782bf8:0
2024-06-04 03:37:31.626 [DBG] SWPR: [WithCoinSelectLock] exited the lock
2024-06-04 03:37:31.656 [DBG] SWPR: Creating sweep transaction 6c4bc2d7afeecb395d8bf0654065d7f5acb52b1017e5b4a61442bbd1dd3d7207 for 100 inputs...

Running with make itest icase=sign_psbt/fund_and_sign_psbt backend=bitcoind,

2024-06-04 03:46:54.785 [INF] RPCS: [sendcoins] addr=2MzDETUurmNbcnx2mLWtm4tdeARCFUkdQbU, amt=0 BTC, sat/kw=12500, min_confs=0, send_all=true
2024-06-04 03:46:54.786 [DBG] SWPR: [WithCoinSelectLock] entered the lock
2024-06-04 03:46:54.856 [DBG] SWPR: [WithCoinSelectLock] finished fetching UTXOs
2024-06-04 03:46:54.856 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: f4436cede2c43faa7eb16cc2d4577e0825790f685b146eacfbe2a07a1006df00:0
...leasing 98 more...
2024-06-04 03:46:55.960 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: 8dd273ce89622e59cae55a216a33b65d581a0d9ea95a30d74138140f5a0d15ff:0
2024-06-04 03:46:55.970 [DBG] SWPR: [WithCoinSelectLock] exited the lock
2024-06-04 03:46:55.984 [DBG] SWPR: Creating sweep transaction c383561e0096a6099dfe5c9cd57a42a6f393cb7fd281e137e5d989c518db3627 for 100 inputs...

Running with make itest icase=sign_psbt/fund_and_sign_psbt backend=bitcoind dbbackend=postgres,

2024-06-04 03:41:21.576 [INF] RPCS: [sendcoins] addr=2N6HM91LmDZP63ViD5MPirXxLScp3gmK2zf, amt=0 BTC, sat/kw=12500, min_confs=0, send_all=true
2024-06-04 03:41:21.577 [DBG] SWPR: [WithCoinSelectLock] entered the lock
2024-06-04 03:41:23.324 [DBG] SWPR: [WithCoinSelectLock] finished fetching UTXOs
2024-06-04 03:41:23.324 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: 38fecbec097297b3e4b1e2f535e4d4707efc8d5668424f4c14e29805aa771801:0
...leasing 98 more...
2024-06-04 03:42:02.574 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: ad3297020e2b81993d2093ae239894a47ad3f67b243fc2f79c0f1fdf808384fc:0
2024-06-04 03:42:03.284 [DBG] SWPR: [WithCoinSelectLock] exited the lock
2024-06-04 03:42:03.772 [DBG] SWPR: Creating sweep transaction e50f98c1f40080ee20139d095945149a16d3334080658598bf4a5eef8ec90a7f for 100 inputs...

Running with make itest icase=sign_psbt/fund_and_sign_psbt backend=bitcoind dbbackend=postgres nativesql=true,

2024-06-04 03:53:42.474 [INF] RPCS: [sendcoins] addr=2MuaBevMSc9Gxdi4WGAnuEiRXH2pGAcYNaj, amt=0 BTC, sat/kw=12500, min_confs=0, send_all=true
2024-06-04 03:53:42.475 [DBG] SWPR: [WithCoinSelectLock] entered the lock
2024-06-04 03:53:44.029 [DBG] SWPR: [WithCoinSelectLock] finished fetching UTXOs
2024-06-04 03:53:44.029 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: 1deb82f888c58b2c9e86d0f8773537324a5b1fe2ddd2b3d3a243088cb9990000:0
...leasing 98 more...
2024-06-04 03:54:19.937 [DBG] SWPR: [WithCoinSelectLock] leasing utxo: a4304be189a3075d22f5cabc638af956da871b09ae46ffb48a6dd1c143d084fe:0
2024-06-04 03:54:20.671 [DBG] SWPR: [WithCoinSelectLock] exited the lock
2024-06-04 03:54:21.260 [DBG] SWPR: Creating sweep transaction a6d8019cb0cb3f5bb0603bcfc4676b6eef81f88301933e75bd67673650b4e1c5 for 100 inputs...

[Roasbeef]

The implementation here is pretty unglamorous: https://github.com/btcsuite/btcwallet/blob/6fe19a472a627b5f3a6ab2eda9ed7d8809d04f2e/wtxmgr/tx.go#L1184-L1204

Perhaps the culprit is that we'll create 100 distributed transactions for the 100 outpoints, instead of just 1 transaction?