Darren/refactor/staker private structs

[darrenkel]

Description

Refactor Validation, Delegation and Aggregation structs to use a private body. This makes the struct read only in other packages. It follows the same pattern as tx.Transaction

Validator Changes: release/v2.4.1...e41ddb8

Delegator Changes: b411ce5

Aggregation Changes: b17655e

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• New and existing E2E tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have not added any vulnerable dependencies to my code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.82838% with 49 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
builtin/staker/validation/validation.go	86.59%	10 Missing and 3 partials ⚠️
builtin/staker/staker.go	81.81%	1 Missing and 5 partials ⚠️
builtin/staker_native.go	64.70%	3 Missing and 3 partials ⚠️
builtin/staker/aggregation/service.go	61.53%	0 Missing and 5 partials ⚠️
builtin/staker/aggregation/aggregation.go	85.18%	1 Missing and 3 partials ⚠️
builtin/staker/delegation/service.go	76.47%	2 Missing and 2 partials ⚠️
builtin/staker/validation/linked_list.go	76.47%	0 Missing and 4 partials ⚠️
builtin/staker/validation/service.go	91.11%	2 Missing and 2 partials ⚠️
builtin/staker/validation/storage.go	71.42%	0 Missing and 2 partials ⚠️
builtin/staker/transition.go	50.00%	0 Missing and 1 partial ⚠️

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