Switch from deprecated serde_yaml to serde_yaml_ng

serde_yaml is deprecated and unmaintained. serde_yaml_ng is the community
fork with a compatible API, so this is a straightforward rename across the
codebase.

Cargo.lock

@@ -304,7 +304,7 @@ dependencies = [
  "regex",
  "serde",
  "serde_json",
- "serde_yaml",
+ "serde_yaml_ng",
  "tempfile",
  "tiktoken-rs",
  "tokio",
@@ -3892,10 +3892,10 @@ dependencies = [
 ]
 
 [[package]]
-name = "serde_yaml"
-version = "0.9.34+deprecated"
+name = "serde_yaml_ng"
+version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6a8b1a1a2ebf674015cc02edccce75287f1a0130d394307b36743c2f5d504b47"
+checksum = "7b4db627b98b36d4203a7b458cf3573730f2bb591b28871d916dfa9efabfd41f"
 dependencies = [
  "indexmap",
  "itoa",