fix: remove int64 limitations

[krogla]

List of changes:

• Use the uint256 type instead of uint64 in NodeOperatorsRegestry to work with node operator validators' data. Validate that the resulting value doesn't exceed the UINT64_MAX in the Packed64x4.set() method.
• Replace calculations on signed variables with equivalent on unsigned int type
• Prevent math operation overflows using SafeMath or asserts before/after calculations

NodeOperatorsRegistry contract size reduced from 23.971 to 23.169 KB

Gase changes for most often used methods based on unit tests

Method Name	Prev Version	New Version
obtainDepositData()	194,414	189,988
onExitedAndStuckValidatorsCountsUpdated()	8,300,043	8,148,381
updateExitedValidatorsCount()	118,450	115,006

[TheDZhon]

@Psirex please consider resolving the conflicts by integrating the changes from the upstream branch (have divergent changes of the lastly pushed commits) 🙏

[TheDZhon]

LGTM 👍

Please consider addressing the minor outdated naming issue