Incorrect behaviour of trees in override_range function

[seemenkina]

1. Full Merkle Tree and Optimal Merkle Tree

This condition will not work correctly if the number of items to insert is less than the number of items to delete

https://github.com/vacp2p/zerokit/blob/4931b252378623bcc6f005164950710d152ee600/utils/src/merkle_tree/full_merkle_tree.rs#L181

At the same time the same behaviour is implemented correctly in PmTree:

https://github.com/vacp2p/zerokit/blob/4931b252378623bcc6f005164950710d152ee600/rln/src/pm_tree_adapter.rs#L287-L288

let leaves_new: Vec<TestFr> = (0..2).map(TestFr::from).collect();
tree.override_range(0, leaves_new.clone(), [0, 1, 2, 3]).unwrap();

2. PmTree

Doesn't work correctly behaviour when we need to put leaves further away than deleted items because of this line:

https://github.com/vacp2p/zerokit/blob/4931b252378623bcc6f005164950710d152ee600/rln/src/pm_tree_adapter.rs#L303-L304

and here should be start instead of min_index

For example: if we want to write data in indices [4..8] and delete data in indices [0..4], the data will be written from index 0 instead of 4.

Example for testing:

let leaves: Vec<Fr> = (0..4).map(|s| Fr::from(s as i32)).collect();
tree.override_range(4, leaves.clone(), [0, 1, 2, 3]).unwrap();

[rymnc]

addressed in https://github.com/vacp2p/zerokit/pull/250