Simplify tool error handling

[Saghen]

Continues #1163 by having tools simplify throw errors rather than returning an explicit error or success status. Also introduced a util for stringifying unknown errors so we'll hopefully find less [Object object] errors downstream from libraries which don't use the native Error object

[mishig25]

the CI is red. For example, these lines

chat-ui/src/lib/server/tools/calculator.ts

Line 1 in ada8a93

import { ToolResultStatus } from "$lib/types/Tool";

chat-ui/src/lib/server/tools/images/editing.ts

Line 3 in ada8a93

import { ToolResultStatus } from "$lib/types/Tool";

is no longer needed

[mishig25]

looks great! Like the new design of throwing errors rather than using rust-like error enums values (looks more javascript-y now)

[mishig25]

there is a merge conflict, afterwards LGTM !

[mishig25]

Fixed the merge conflicts. LGTM! Merging it.

simulated a prod error (testing)

on main

on this branch

one small follow-up PR we can do is: like #1188, we can improve the UI when there is an error (as an example, like red background color on error msg etc. cc: @gary149)