Add and update rewards to open challenges lacking one (model-checking#459)

Proposes a reward of 10k USD for several challenges and 20k for the
larger ones among them.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

---------

Co-authored-by: Felipe R. Monteiro <[email protected]>

Author: tautschnig

doc/src/challenges/0002-intrinsics-memory.md

@@ -4,7 +4,7 @@
 - **Tracking Issue:** [#16](https://github.com/model-checking/verify-rust-std/issues/16)
 - **Start date:** *2024/06/12*
 - **End date:** *2025/04/10*
-- **Reward:** *N/A*
+- **Reward:** *10000 USD*
 
 -------------------
 

doc/src/challenges/0005-linked-list.md

@@ -4,7 +4,7 @@
 - **Tracking Issue:** [#29](https://github.com/model-checking/verify-rust-std/issues/29)
 - **Start date:** *2024/07/01*
 - **End date:** *2025/08/12*
-- **Reward:** *5,000 USD*
+- **Reward:** *20000 USD*
 - **Contributors:** [Bart Jacobs](https://github.com/btj)
 
 -------------------

doc/src/challenges/0010-string.md

@@ -4,7 +4,7 @@
 - **Tracking Issue:** [#61](https://github.com/model-checking/verify-rust-std/issues/61)
 - **Start date:** *2024/08/19*
 - **End date:** *2025/04/10*
-- **Reward:** *N/A*
+- **Reward:** *10000 USD*
 
 -------------------
 

doc/src/challenges/0012-nonzero.md

@@ -4,7 +4,7 @@
 - **Tracking Issue:** [#71](https://github.com/model-checking/verify-rust-std/issues/71)
 - **Start date:** *2024/08/23*
 - **End date:** *2025/04/10*
-- **Reward:** *N/A*
+- **Reward:** *10000 USD*
 
 -------------------
 

doc/src/challenges/0013-cstr.md

@@ -5,7 +5,7 @@
 - **Tracking Issue:** [#150](https://github.com/model-checking/verify-rust-std/issues/150)
 - **Start date:** *2024/11/04*
 - **End date:** *2025/04/10*
-- **Reward:** *N/A*
+- **Reward:** *10000 USD*
 
 -------------------
 ## Goal

doc/src/challenges/0015-intrinsics-simd.md

@@ -1,11 +1,11 @@
 # Challenge 15: Contracts and Tests for SIMD Intrinsics
 
 - **Status:** Open
-- **Reward:** 
 - **Solution:** 
 - **Tracking Issue:** [#173](https://github.com/model-checking/verify-rust-std/issues/173)
 - **Start date:** 2025/02/01
 - **End date:** 2025/08/01
+- **Reward:** *20000 USD*
 
 -------------------
 

doc/src/challenges/0022-str-iter.md

@@ -4,7 +4,7 @@
 - **Tracking Issue:** [#279](https://github.com/model-checking/verify-rust-std/issues/279)
 - **Start date:** *2025-03-07*
 - **End date:** *2025-10-17*
-- **Reward:** *10000*
+- **Reward:** *10000 USD*
 
 -------------------