rustPlatform: --frozen -> --offline

--frozen is stricter than we need in Nixpkgs.  If a Cargo.lock is
slightly wrong, or (in my use case) if building a subproject that is
not a member of the top-level workspace, but the correct Cargo.lock
can be entirely resolved from the existing top-level Cargo.lock, it
should be deterministic, and shouldn't cause any problems, to let
cargo generate the new Cargo.lock.  This should result in less need to
bother upstreams about fixing their Cargo.lock files in cases where
they could have been automatically fixed.

pkgs/build-support/rust/hooks/cargo-build-hook.sh

@@ -39,7 +39,7 @@ cargoBuildHook() {
     set -x
     @setEnv@ cargo build -j $NIX_BUILD_CORES \
         --target @rustHostPlatformSpec@ \
-        --frozen \
+        --offline \
         ${cargoBuildProfileFlag} \
         ${cargoBuildNoDefaultFeaturesFlag} \
         ${cargoBuildFeaturesFlag} \

pkgs/build-support/rust/hooks/cargo-check-hook.sh

@@ -29,7 +29,7 @@ cargoCheckHook() {
     fi
 
     argstr="${cargoCheckProfileFlag} ${cargoCheckNoDefaultFeaturesFlag} ${cargoCheckFeaturesFlag}
-        --target @rustHostPlatformSpec@ --frozen ${cargoTestFlags}"
+        --target @rustHostPlatformSpec@ --offline ${cargoTestFlags}"
 
     (
         set -x

pkgs/build-support/rust/hooks/cargo-nextest-hook.sh

@@ -29,7 +29,7 @@ cargoNextestHook() {
     fi
 
     argstr="${cargoCheckProfileFlag} ${cargoCheckNoDefaultFeaturesFlag} ${cargoCheckFeaturesFlag}
-        --target @rustHostPlatformSpec@ --frozen ${cargoTestFlags}"
+        --target @rustHostPlatformSpec@ --offline ${cargoTestFlags}"
 
     (
         set -x

pkgs/build-support/rust/hooks/maturin-build-hook.sh

@@ -11,7 +11,7 @@ maturinBuildHook() {
     set -x
     @setEnv@ maturin build \
         --jobs=$NIX_BUILD_CORES \
-        --frozen \
+        --offline \
         --target @rustTargetPlatformSpec@ \
         --manylinux off \
         --strip \