Bump Rust to 1.75 (#3815)

**This PR also bumps wasmtime version from 0.38 to 2.0 as 0.38 does not
build with Rust 1.75**. I did not test the plugin runtime as (AFAIK) we
intend to deprecate it; also, wasmtime's most recent version is 16.0, so
it'd make sense to bump the version at some point anyways. I did not
bump the version to 16.0 straight away as that'd require code changes in
`plugin_runtime`.
Release Notes:

- N/A

crates/plugin_runtime/Cargo.toml

@@ -5,9 +5,9 @@ edition = "2021"
 publish = false
 
 [dependencies]
-wasmtime = "0.38"
-wasmtime-wasi = "0.38"
-wasi-common = "0.38"
+wasmtime = "2.0"
+wasmtime-wasi = "2.0"
+wasi-common = "2.0"
 anyhow.workspace = true
 serde.workspace = true
 serde_derive.workspace = true
@@ -17,4 +17,4 @@ pollster = "0.2.5"
 smol.workspace = true
 
 [build-dependencies]
-wasmtime = { version = "0.38", features = ["all-arch"] }
+wasmtime = { version = "2.0", features = ["all-arch"] }