Support passing a specific block in morley-client along with some additional improvements

Description

Problem: we need to access some data at specific blocks, but currently morley-client always assumes head block.

Solution:

• Add BlockId type.
• Generalize some methods to have BlockId argument.
• Keep versions that pass head with their existing names to avoid breaking something.

Also I added a couple of other things (see commit messages) and removed an old workaround.

Related issue(s)

None, I need it for another project.

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • Root README and other README.md files
    • Haddock
    • docs/
  • I updated changelog files of all affected packages released to Hackage if my changes are externally visible.

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• My commits comply with the following policy.
• My code complies with the style guide.