docs: Correct default-unwind Cargo.toml examples

The examples for configuring `default-unwind` inside Cargo.toml files
use unquoted integers. This isn't how they are actually expected to be
written, and following these examples leads to kani failing to run.

This corrects the examples in the documentation to align with the
expected configuration format.

Signed-off-by: hashcatHitman <[email protected]>

Author: hashcatHitman

docs/src/tutorial-loop-unwinding.md

@@ -112,7 +112,7 @@ You can do this by putting this into your `Cargo.toml` file:
 
 ```toml
 [workspace.metadata.kani.flags]
-default-unwind = 1
+default-unwind = "1"
 ```
 
 ## Bounded proof

docs/src/usage.md

@@ -61,7 +61,7 @@ For example, if you want to set a default loop unwinding bound (when it's not ot
 
 ```toml
 [package.metadata.kani.flags]
-default-unwind = 1
+default-unwind = "1"
 ```
 
 The options here are the same as on the command line (`cargo kani --help`), and flags (that is, command line arguments that don't take a value) are enabled by setting them to `true`.