udpate signed delegate types

[bz888]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Update SignedDelegateAction type in accordance to docs
https://github.com/near/NEPs/blob/a5bb580a037cde12017d594a6fa0a817c748de32/specs/RuntimeSpec/Actions.md?plain=1#L348

Signature is outputted as a string, during runtime.

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• I have tested locally
• I have performed a self review of my changes
• Updated any relevant documentation
• Linked to any relevant issues
• I have added tests relevant to my changes
• Any dependent changes have been merged and published in downstream modules
• My code is up to date with the base branch
• I have updated relevant changelogs. We suggest using chan

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🔴	Statements	34.57%	1292/3737
🔴	Branches	54.7%	64/117
🔴	Functions	13.85%	18/130
🔴	Lines	34.57%	1292/3737

Test suite run success

9 tests passing in 3 suites.

Report generated by 🧪jest coverage report action from a754297