TRST audit fixes for HorizonStaking contract

[Maikol]

This PR fixes the following issues:

• TRST-H-2 Core thawing logic of Horizon staking can be broken due to collision in data structures
• TRST-H-3 An attacker could prevent a delegator from ever withdrawing their tokens
• TRST-H-4 The last withdrawal from a provision or delegation could permanently revert due to accounting flaw in slashing
• TRST-H-6 During the transition period, legacy allocations cannot be slashed
• TRST-H-7 Delegators that began undelegation before the transition would not be able to withdraw them
• TRST-M-3 An attacker could make the minimum delegation amount arbitrarily large and prevent competing delegations
• TRST-M-11 After the transition period, locked amount would still not be available for use
• TRST-M-12 The operator check in closeAllocations() will not work, indexers must close by themselves
• TRST-L-3 The getThawedTokens() function could return a wrong amount leading to integration risks
• TRST-R-1 Improve event structure
• TRST-R-7 Thawing shares should be rounded up to protect from early unlocking of tokens
• TRST-R-9 Documentation errors

[openzeppelin-code]

TRST audit fixes for HorizonStaking contract

Generated at commit: f6ce0166ef1fc09d6be3835424ba6e258c6fc894

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	2 4 0 15 39 60
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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For more details view the full report in OpenZeppelin Code Inspector

[tmigone]

Some suggestions!