fix(tokens/token-swap): deposit ratio bug

[a-hariti]

In the Token Swap program example,

The current deposit_liquidity instruction checks the existing liquidity to establish a tokenA/tokenB ratio, but it has a bug.

program-examples/tokens/token-swap/anchor/programs/token-swap/src/instructions/deposit_liquidity.rs

Lines 40 to 60 in 8e0879b

	let ratio = I64F64::from_num(pool_a.amount)
	.checked_mul(I64F64::from_num(pool_b.amount))
	.unwrap();
	if pool_a.amount > pool_b.amount {
	(
	I64F64::from_num(amount_b)
	.checked_mul(ratio)
	.unwrap()
	.to_num::<u64>(),
	amount_b,
	)
	} else {
	(
	amount_a,
	I64F64::from_num(amount_a)
	.checked_div(ratio)
	.unwrap()
	.to_num::<u64>(),
	)
	}
	};

Specifically here (notice the multiplication instead of division)

 let ratio = I64F64::from_num(pool_a.amount) 
         .checked_mul(I64F64::from_num(pool_b.amount)) 
         .unwrap(); 

I fixed that and added a tests to verify the desired behavior:

1. deposit the same ratio as the pool
2. handle deposits of a different ratio