Extract light clients into separate crates

[hu55a1n1]

Closes: #XXX

Description

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PR author checklist:

• Added changelog entry, using unclog.
• Added tests: integration (for Hermes) or unit/mock tests (for modules).
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[adizere]

For future reference: ADR 011 (PR #2356) describes why we closed un-merged the present PR, briefly:

The present PR attempted to break the circular dependencies [between light client and ibc crate] by extracting all core code (types, traits, etc.) that a light client implementation would possibly need into a separate crate, say ibc-base, and then have both the ibc modules crate and light client implementation crates depend on that ibc-base crate. This was implemented in PR #2327, but the solution seems to be fragile and unmaintainable.