Rename RelayState to RelayManager for clarity

[0xZaddyy]

This pull request renames RelayState to RelayManager to better reflect its role in the codebase as a manager rather than just a state holder.

No other changes were made, this PR is focused solely on the renaming.

Closes #724

[benalleng]

uTACK thanks this looks good!

[DanGould]

ACK 4f3655e

ensured no relay_state/RelayState remain

[coveralls]

Pull Request Test Coverage Report for Build 15376703385

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 6 of 8 (75.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.592%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
payjoin-cli/src/app/v2/ohttp.rs	3	5	60.0%

Totals
Change from base Build 15354051252:	0.0%
Covered Lines:	6539
Relevant Lines:	7730

---

💛 - Coveralls