psbt: add new fields for MuSig2

[guggero]

Implements the new input and output fields to the PSBT library according to the (non-merged) BIP-0373.

Opening as draft PR because the following features are not yet implemented:

• Support MuSig2 partial signatures in Updater.Sign()
• Support MuSig2 partial signatures in the finalizer

[coveralls]

Pull Request Test Coverage Report for Build 9513655947

Details

• 4 of 240 (1.67%) changed or added relevant lines in 3 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 56.774%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcutil/psbt/partial_output.go	1	22	4.55%
btcutil/psbt/partial_input.go	3	63	4.76%
btcutil/psbt/musig2.go	0	155	0.0%

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	3	86.27%

Totals
Change from base Build 9348961734:	-0.2%
Covered Lines:	29625
Relevant Lines:	52181

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9519109524

Details

• 4 of 381 (1.05%) changed or added relevant lines in 5 files are covered.
• 8 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.4%) to 56.6%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcutil/psbt/partial_output.go	1	22	4.55%
btcutil/psbt/utils.go	0	22	0.0%
btcutil/psbt/partial_input.go	3	63	4.76%
btcutil/psbt/finalizer.go	0	119	0.0%
btcutil/psbt/musig2.go	0	155	0.0%

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	3	86.27%
txscript/taproot.go	5	95.31%

Totals
Change from base Build 9348961734:	-0.4%
Covered Lines:	29614
Relevant Lines:	52322

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9528732501

Details

• 4 of 381 (1.05%) changed or added relevant lines in 5 files are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.4%) to 56.603%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcutil/psbt/partial_output.go	1	22	4.55%
btcutil/psbt/utils.go	0	22	0.0%
btcutil/psbt/partial_input.go	3	63	4.76%
btcutil/psbt/finalizer.go	0	119	0.0%
btcutil/psbt/musig2.go	0	155	0.0%

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	2	87.32%
peer/peer.go	9	73.72%

Totals
Change from base Build 9348961734:	-0.4%
Covered Lines:	29616
Relevant Lines:	52322

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9528834149

Details

• 4 of 381 (1.05%) changed or added relevant lines in 5 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.4%) to 56.626%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcutil/psbt/partial_output.go	1	22	4.55%
btcutil/psbt/utils.go	0	22	0.0%
btcutil/psbt/partial_input.go	3	63	4.76%
btcutil/psbt/finalizer.go	0	119	0.0%
btcutil/psbt/musig2.go	0	155	0.0%

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	3	86.97%

Totals
Change from base Build 9348961734:	-0.4%
Covered Lines:	29628
Relevant Lines:	52322

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9528865705

Details

• 4 of 387 (1.03%) changed or added relevant lines in 5 files are covered.
• 12 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.4%) to 56.607%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcutil/psbt/partial_output.go	1	22	4.55%
btcutil/psbt/utils.go	0	22	0.0%
btcutil/psbt/partial_input.go	3	63	4.76%
btcutil/psbt/finalizer.go	0	125	0.0%
btcutil/psbt/musig2.go	0	155	0.0%

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	3	86.27%
peer/peer.go	9	73.72%

Totals
Change from base Build 9348961734:	-0.4%
Covered Lines:	29621
Relevant Lines:	52327

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9528900206

Details

• 6 of 389 (1.54%) changed or added relevant lines in 5 files are covered.
• 12 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.4%) to 56.587%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
btcutil/psbt/partial_output.go	1	22	4.55%
btcutil/psbt/utils.go	0	22	0.0%
btcutil/psbt/partial_input.go	3	63	4.76%
btcutil/psbt/finalizer.go	2	127	1.57%
btcutil/psbt/musig2.go	0	155	0.0%

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	3	86.27%
peer/peer.go	9	73.49%

Totals
Change from base Build 9348961734:	-0.4%
Covered Lines:	29611
Relevant Lines:	52328

---

💛 - Coveralls