[ty] Fix some configuration panics in the LSP (#22040)

## Summary

This is a revival of https://github.com/astral-sh/ruff/pull/21047 now
that we have a reproducer again.

* Fixes https://github.com/astral-sh/ty/issues/2031
* Fixes https://github.com/astral-sh/ty/issues/859

## Test Plan

e2e test from @zanieb

---------

Co-authored-by: Zanie Blue <contact@zanie.dev>

crates/ty_python_semantic/src/program.rs

@@ -163,6 +163,17 @@ impl Default for PythonVersionWithSource {
     }
 }
 
+#[derive(PartialEq, Eq, Debug, Copy, Clone, get_size2::GetSize)]
+pub enum MisconfigurationMode {
+    /// Settings Failure Is Not An Error.
+    ///
+    /// This is used by the default database, which we are incentivized to make infallible,
+    /// while still trying to "do our best" to set things up properly where we can.
+    UseDefault,
+    /// Settings Failure Is An Error.
+    Fail,
+}
+
 /// Configures the search paths for module resolution.
 #[derive(Eq, PartialEq, Debug, Clone)]
 pub struct SearchPathSettings {
@@ -187,6 +198,9 @@ pub struct SearchPathSettings {
     /// We should ideally only ever use this for things like goto-definition,
     /// where typeshed isn't the right answer.
     pub real_stdlib_path: Option<SystemPathBuf>,
+
+    /// How to handle apparent misconfiguration
+    pub misconfiguration_mode: MisconfigurationMode,
 }
 
 impl SearchPathSettings {
@@ -204,6 +218,7 @@ impl SearchPathSettings {
             custom_typeshed: None,
             site_packages_paths: vec![],
             real_stdlib_path: None,
+            misconfiguration_mode: MisconfigurationMode::Fail,
         }
     }