v2.0: fix: borrow stakes delegation during snapshot serialization (backport of #2455)

[mergify]

Problem

When serializing snapshots, we do a full deep clone of the stake delegations when serializing Stakes<Delegation>. As of v2.1 this serialization flow is limited to serializing the stakes cache since epoch stakes are serialized with versioned epoch stakes as of #2282.

Summary of Changes

Build a shallow copy of stake delegations by borrowing the delegation field from the stake accounts to avoid allocating so much when serializing Stakes<Delegation> during snapshot creation.

Fixes #

---

This is an automatic backport of pull request #2455 done by [Mergify](https://mergify.com).

[mergify]

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Changes to be committed:
	modified:   runtime/src/bank.rs
	modified:   runtime/src/bank/partitioned_epoch_rewards/calculation.rs
	modified:   runtime/src/stake_account.rs
	new file:   runtime/src/stakes/serde_stakes.rs
	modified:   sdk/program/src/stake/state.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   runtime/src/bank/serde_snapshot.rs
	both modified:   runtime/src/stakes.rs

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[jstarry]

rebased on v2.0 to pickup latest cargo version

[jstarry]

Oh still waiting on #2518 to be merged

[mergify]

The Firedancer team maintains a line-for-line reimplementation of the
native programs, and until native programs are moved to BPF, those
implementations must exactly match their Agave counterparts.
If this PR represents a change to a native program implementation (not
tests), please include a reviewer from the Firedancer team. And please
keep refactors to a minimum.