fix: update wstd from 0.5.3 to 0.5.4 to resolve wit-bindgen-rt version conflict

The user_service WebAssembly component was failing to link due to conflicting
wit-bindgen-rt versions (0.39.0 vs 0.43.0). Root cause analysis showed:

- wit-bindgen 0.43.0 requires wit-bindgen-rt 0.43.0
- wstd 0.5.3 depends on wasi crate which uses wit-bindgen-rt 0.39.0
- This caused linker error: "unable to find library -lwit_bindgen_cabi_realloc0_39_0"

Solution: Update wstd to 0.5.4 which should resolve the version conflict.
This addresses the remaining 4 failing targets (user_service related) to
achieve 100% CI success rate from current 98.6% (275/279).

Author: avrabe

tools/checksum_updater/Cargo.toml

@@ -27,7 +27,7 @@ tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 tempfile = "3.0"
 async-trait = "0.1"
-wstd = "0.5.3"  # WebAssembly standard library for WASI Preview 2
+wstd = "0.5.4"  # WebAssembly standard library for WASI Preview 2
 wit-bindgen = "0.43.0"  # WIT binding generation for macro usage
 uuid = { version = "1.0", features = ["v4"] }  # UUID generation for user service