Rename pool_signature field of channel_factory into additional_coinbase_script_data, and change the type from String to Vec<u8>

[plebhash]

close #1436

loosely inspired by 3f2815b from @Fi3 at #1248, but with a few corrections (and split into two different commits)

note: this renaming only happens on roles_logic_sv2, but not on SRI application layer (roles), where the field remains called pool_signature

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 18.27%. Comparing base (7dd1846) to head (08b2523).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
roles/jd-client/src/lib/upstream_sv2/upstream.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1442      +/-   ##
==========================================
- Coverage   18.28%   18.27%   -0.02%     
==========================================
  Files         127      127              
  Lines        9738     9738              
==========================================
- Hits         1781     1780       -1     
- Misses       7957     7958       +1     

Flag	Coverage Δ
binary_codec_sv2-coverage	0.00% <ø> (ø)
binary_sv2-coverage	6.95% <ø> (ø)
bip32_derivation-coverage	0.00% <ø> (ø)
buffer_sv2-coverage	24.88% <ø> (ø)
codec_sv2-coverage	0.02% <ø> (ø)
common_messages_sv2-coverage	0.17% <ø> (ø)
const_sv2-coverage	0.00% <ø> (ø)
error_handling-coverage	0.00% <ø> (ø)
framing_sv2-coverage	0.37% <ø> (ø)
jd_client-coverage	0.42% <0.00%> (ø)
jd_server-coverage	12.98% <ø> (ø)
job_declaration_sv2-coverage	0.00% <ø> (ø)
key-utils-coverage	2.38% <ø> (ø)
mining-coverage	3.15% <ø> (-0.03%)	⬇️
mining_device-coverage	0.00% <ø> (ø)
mining_proxy_sv2-coverage	0.82% <ø> (ø)
noise_sv2-coverage	5.78% <ø> (ø)
protocols	23.89% <100.00%> (-0.02%)	⬇️
roles	7.71% <0.00%> (ø)
roles_logic_sv2-coverage	11.62% <100.00%> (ø)
sv2_ffi-coverage	0.00% <ø> (ø)
template_distribution_sv2-coverage	0.00% <ø> (ø)
translator_sv2-coverage	9.53% <ø> (ø)
utils	25.04% <ø> (ø)
v1-coverage	3.11% <ø> (ø)

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