256-bit host fn docs say errors returned when they trap

[leighmcculloch]

The 256-bit maths host fns say in their docs that an error is returned, but from the guest perspective no error is returned rather a trap occurs.

rs-soroban-env/soroban-env-common/env.json

Lines 443 to 697 in 97546e0

	{
	"export": "n",
	"name": "u256_add",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U256Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked integer addition. Computes `lhs + rhs`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "o",
	"name": "u256_sub",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U256Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked integer subtraction. Computes `lhs - rhs`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "p",
	"name": "u256_mul",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U256Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked integer multiplication. Computes `lhs * rhs`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "q",
	"name": "u256_div",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U256Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked integer division. Computes `lhs / rhs`, returning `ScError` if `rhs == 0` or overflow occurred. "
	},
	{
	"export": "r",
	"name": "u256_rem_euclid",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U256Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked Euclidean modulo. Computes `lhs % rhs`, returning `ScError` if `rhs == 0` or overflow occurred. "
	},
	{
	"export": "s",
	"name": "u256_pow",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U32Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked exponentiation. Computes `lhs.exp(rhs)`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "t",
	"name": "u256_shl",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U32Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked shift left. Computes `lhs << rhs`, returning `ScError` if `rhs` is larger than or equal to the number of bits in `lhs`."
	},
	{
	"export": "u",
	"name": "u256_shr",
	"args": [
	{
	"name": "lhs",
	"type": "U256Val"
	},
	{
	"name": "rhs",
	"type": "U32Val"
	}
	],
	"return": "U256Val",
	"docs": "Performs checked shift right. Computes `lhs >> rhs`, returning `ScError` if `rhs` is larger than or equal to the number of bits in `lhs`."
	},
	{
	"export": "v",
	"name": "i256_add",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "I256Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked integer addition. Computes `lhs + rhs`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "w",
	"name": "i256_sub",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "I256Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked integer subtraction. Computes `lhs - rhs`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "x",
	"name": "i256_mul",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "I256Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked integer multiplication. Computes `lhs * rhs`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "y",
	"name": "i256_div",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "I256Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked integer division. Computes `lhs / rhs`, returning `ScError` if `rhs == 0` or overflow occurred. "
	},
	{
	"export": "z",
	"name": "i256_rem_euclid",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "I256Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked Euclidean modulo. Computes `lhs % rhs`, returning `ScError` if `rhs == 0` or overflow occurred. "
	},
	{
	"export": "A",
	"name": "i256_pow",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "U32Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked exponentiation. Computes `lhs.exp(rhs)`, returning `ScError` if overflow occurred. "
	},
	{
	"export": "B",
	"name": "i256_shl",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "U32Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked shift left. Computes `lhs << rhs`, returning `ScError` if `rhs` is larger than or equal to the number of bits in `lhs`."
	},
	{
	"export": "C",
	"name": "i256_shr",
	"args": [
	{
	"name": "lhs",
	"type": "I256Val"
	},
	{
	"name": "rhs",
	"type": "U32Val"
	}
	],
	"return": "I256Val",
	"docs": "Performs checked shift right. Computes `lhs >> rhs`, returning `ScError` if `rhs` is larger than or equal to the number of bits in `lhs`."

Typically the env.json docs are written from the perspective of the guest, and fns that trap typically say Traps if ....

rs-soroban-env/soroban-env-common/env.json

Line 794 in 97546e0

"docs": "Get the value for a key from a map. Traps if key is not found."

We should update the docs to indicate the maths fns trap.

Originally posted by @leighmcculloch in #1659