Support @fromfile option values in the Rust options parser. (#20634)

As part of this, streamlines away some previous function pointer
clunkiness via a new `Parseable` trait that implements parsing
of scalars and list of scalars for the scalar types bool/i64/f64/String.

While messing with this code: this change also implements the 
"source" field for list- and dict-valued option values.
Previously this was only provided for scalar-valued options. However
the highest-priority source is still a valid and useful concept even
for compound values that might be composed across multiple sources.

src/rust/engine/Cargo.toml

@@ -300,6 +300,7 @@ serde = "1.0.160"
 serde_derive = "1.0.98"
 serde_json = "1.0"
 serde_test = "1.0"
+serde_yaml = "0.9"
 sha2 = "0.10"
 shell-quote = "0.3.0"
 shellexpand = "2.1"

src/rust/engine/options/Cargo.toml

@@ -14,6 +14,9 @@ shellexpand = { workspace = true }
 toml = { workspace = true }
 regex = { workspace = true }
 whoami = { workspace = true }
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }
+serde_yaml = { workspace = true }
 
 [dev-dependencies]
 tempfile = { workspace = true }