Add minimum to attach unused gas in Promise

[ilblackdragon]

Currently when calling with_unused_gas_weight there is no way to validate that there is enough gas left. Add optional argument to specify minimum unused gas that should left - otherwise it should panic with not enough gas.

[frol]

@ilblackdragon Actually, if you specify with_static_gas in addition to with_unused_gas_weight, you can define the minimum attached gas (in the with_static_gas).

Here are a few usages in the wild:

1. near-sdk-rs/near-contract-standards/src/fungible_token/core_impl.rs

   Lines 141 to 149 in dc041fa

   	ext_ft_receiver::ext(receiver_id.clone())
   	// forward all remaining gas to `ft_on_transfer`
   	.with_unused_gas_weight(1)
   	.ft_on_transfer(sender_id.clone(), amount.into(), msg)
   	.then(
   	ext_ft_resolver::ext(env::current_account_id())
   	.with_static_gas(GAS_FOR_RESOLVE_TRANSFER)
   	// do not distribute remaining gas for `ft_resolve_transfer`
   	.with_unused_gas_weight(0)

2. https://github.com/keypom/keypom/blob/ac50caba6568bf1d1334bcd51f37e9cea31d0181/contract/src/drop_claiming/claims.rs#L111-L112

Yet, it is really not intuitive, so we need to:

1. Document the behavior (there is currently little to no documentation on with_unused_gas_weight and with_static_gas, let alone how the combination work)
2. Try to design better API for expressing this usecase

[ilblackdragon]

Yeah, I kind of figured that out diving into the code. But yeah something like with_used_gas_weight(weight, min_gas) would be way better interface