Bump electrsd to 0.26 + bitcoind_25_0 and fix msrv errors

[notmandatory]

This PR bumps electrsd to 0.26 and replaces temporary dependency on bitcoin-internals with hex-conservative as done in #75. Fixed CI MSRV issues with dev dependencies blocking #75 and #74.

[notmandatory]

For some reason with the default feature set the tests aren't completing so I moved this to draft until I get that figured out.

[coveralls]

Pull Request Test Coverage Report for Build 7777789071

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-1.1%) to 78.934%

---

Files with Coverage Reduction	New Missed Lines	%
src/lib.rs	1	97.49%
src/api.rs	10	14.49%
<!--	Total:	11		-->

Totals
Change from base Build 7383678843:	-1.1%
Covered Lines:	918
Relevant Lines:	1163

---

💛 - Coveralls

[notmandatory]

To get the default feature tests to run without locking up I had to limit test threads to 1.

[storopoli]

To get the default feature tests to run without locking up I had to limit test threads to 1.

Have you tried 2? I've managed to get away with 2 in GH Action runners in the past.

[notmandatory]

To get the default feature tests to run without locking up I had to limit test threads to 1.

Have you tried 2? I've managed to get away with 2 in GH Action runners in the past.

Two would probably work, but it runs fast enough with 1 so I don't see a need to push it.