fix: returns descriptive error in case no sequencer registered on the hub

[mtsitrin]

PR Standards

Opening a pull request should be able to meet the following requirements:

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For Author:

• Targeted PR against correct branch
• included the correct type prefix in the PR title
• Linked to Github issue with discussion and accepted design
• Targets only one github issue
• Wrote unit and integration tests
• All CI checks have passed
• Added relevant godoc comments

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For Reviewer:

• confirmed the correct type prefix in the PR title
• Reviewers assigned
• confirmed all author checklist items have been addressed

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After reviewer approval:

• In case targets main branch, PR should be squashed and merged.
• In case PR targets a release branch, PR should be rebased.

[codecov]

Codecov Report

Merging #305 (b5b1808) into main (c217bda) will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #305      +/-   ##
==========================================
+ Coverage   52.18%   52.30%   +0.12%     
==========================================
  Files          70       70              
  Lines       12570    12566       -4     
==========================================
+ Hits         6560     6573      +13     
+ Misses       5078     5066      -12     
+ Partials      932      927       -5     

Impacted Files	Coverage Δ
settlement/base.go	79.87% <ø> (+0.51%)	⬆️
settlement/dymension/dymension.go	21.53% <ø> (+0.23%)	⬆️

... and 2 files with indirect coverage changes

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