lq: Add taproot channel support for elements

[cdecker]

libwally did not support signing taproot outputs until
recently. This means that on elements-based networks we would
default to the legacy non-taproot channels.

Since libwally recently gained support for signing taproot outputs
we can remove support for legacy channels altogether now. This is also
a requirement to work with the VLS signer, which no longer supports
legacy channels either.

Depends-On: #8098 #8158

[cdecker]

Following the upgrade of libwally we now have the vast majority of tests passing, with the exception of a few. There is even a crash, in which the hsmd is refusing to sign an htlc_tx_mingle transaction, potentially due to one of the inputs spent being a taproot output.

My current status is the following:

• I'm testing test_htlc_in_timeout, which exercises the crash
• Building and testing is done via TEST_NETWORK=liquid-regtest poetry run ./configure && poetry run make && poetry run pytest tests -sk test_htlc_in_timeout.
• Attaching gdb to the lightning-2 hsmd:

 gdb -ex "attach $(pstree -p $(pgrep -f lightning-2) | grep lightning_hsmd | grep -oE '[0-9]+')"

• Then breaking at the message in question b handle_sign_htlc_tx_mingle

I found the following so far:

• The call to wally_psbt_sign here fails for input 1, which matches utxo[0] that is passed along. close_info on the utxo is NULL, which isn't surprising as it is not a close.
• The output being spent is a taproot output, so either we're spending via keypath, or we're missing some information hidden in the taptree.
• The entire calltree ends in wally_psbt_get_input_signature_hash on this input 1
• The last message lightningd emits is: We want to bump HTLC fee more, but ran out of funds!

Backtrace:

#0  wally_psbt_get_input_signature_hash (psbt=0x561dba6b9308, index=1, tx=0x561dba6b6608,
    script=0x561dba6bba58 "Q \336y\227%\037Uf\375\060\247\321\354\270Q\205UKQd\303b\037|>\r\332\034\351\233zY`\033\314!\273t²1K\002\020=\227\243\061", script_len=34, flags=0, bytes_out=0x7ffd1879f440 "_\365y\030\375\177", len=32)
    at ../../../libwally-core/src/psbt.c:4582
#1  0x0000561dae3f06e6 in wally_psbt_sign_bip32 (psbt=0x561dba6b9308, hdkey=0x7ffd1879f4e0, flags=20) at ../../../libwally-core/src/psbt.c:4775
#2  0x0000561dae3f07ef in wally_psbt_sign (psbt=0x561dba6b9308, priv_key=0x7ffd1879f630 "r\203/\006\237\331n\330\337o\246\236'mc\315\025\210", priv_key_len=32, flags=4) at ../../../libwally-core/src/psbt.c:4801
#3  0x0000561dae3ac894 in sign_our_inputs (utxos=0x561dba6be448, psbt=0x561dba6b9308) at hsmd/libhsmd.c:593
#4  0x0000561dae3abefe in handle_sign_htlc_tx_mingle (c=c@entry=0x561dba6b54d8, msg_in=msg_in@entry=0x561dba6bc358 "") at hsmd/libhsmd.c:1757
#5  0x0000561dae3a90fa in hsmd_handle_client_message (ctx=<optimized out>, client=0x561dba6b54d8, msg=0x561dba6bc358 "") at hsmd/libhsmd.c:2223
#6  0x0000561dae39e2da in handle_client (conn=0x561dba6b4e28, c=0x561dba6b4ba8) at hsmd/hsmd.c:719
#7  0x0000561dae480fbd in next_plan (conn=0x561dba6b4e28, plan=0x561dba6b4e48) at ccan/ccan/io/io.c:60
#8  do_plan (conn=conn@entry=0x561dba6b4e28, plan=plan@entry=0x561dba6b4e48, idle_on_epipe=false) at ccan/ccan/io/io.c:422
#9  0x0000561dae480ebd in io_ready (conn=conn@entry=0x561dba6b4e28, pollflags=1) at ccan/ccan/io/io.c:439
#10 0x0000561dae482742 in io_loop (timers=timers@entry=0x0, expired=expired@entry=0x0) at ccan/ccan/io/poll.c:455
#11 0x0000561dae39dfe3 in main (argc=3, argv=0x7ffd1879f988) at hsmd/hsmd.c:801