Add directory server fallback for improved network resilience

[0xZaddyy]

This PR introduces a robust directory fallback system, Implements multiple directory server support with automatic fallback to address the critical single point of failure identified in issue #1007.

Pull Request Checklist

Please confirm the following before requesting review:

• I have disclosed my use of
  AI
  in the body of this PR.
• I have read CONTRIBUTING.md and rebased my branch to produce hygienic commits.

[coveralls]

Pull Request Test Coverage Report for Build 21283165275

Details

• 34 of 56 (60.71%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 83.169%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
payjoin-cli/src/app/config.rs	5	6	83.33%
payjoin-cli/src/app/v2/ohttp.rs	29	50	58.0%

Totals
Change from base Build 21267453749:	-0.03%
Covered Lines:	10145
Relevant Lines:	12198

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💛 - Coveralls