ci: remove cargo _targets caches everywhere

This MR removes Cargo target directory caching from all build jobs across the CI infrastructure.

Key Changes

Cache Configuration Removed:

• removed _target-associated variable from the scripts/ci/datadog_send_job_cache_info.sh script

CI Library Changes:

• ci/lib_cacio/cacio.ml & ci/lib_cacio/cacio.mli: Removed cargo_target_caches parameter from job definitions
• ci/lib_tezos_ci/tezos_ci.ml & ci/lib_tezos_ci/tezos_ci.mli: Removed enable_cargo_target_caches function
• ci/lib_tezos_ci_jobs/common.ml: Removed calls to enable_cargo_target_caches
• etherlink/ci/etherlink_ci.ml: Removed cargo_target_caches:true parameter
• rollup_node/ci/rollup_node_ci.ml: Removed cargo_target_caches:true parameter

Modified Jobs

The following jobs were modified across all pipeline configurations:

Core Build Jobs:

• oc.build_arm64-released
• oc.build_x86_64-released
• oc.build:static-x86_64-linux-binaries
• oc.build:static-arm64-linux-binaries

Etherlink Jobs:

• etherlink.build_tezt
• etherlink.build_evm_node_static_arm64
• etherlink.build_evm_node_static_x86_64

Smart Rollup Node Jobs:

• octez-smart-rollup-node.build:static-arm64-binaries
• octez-smart-rollup-node.build:static-x86_64-binaries

Impact

This change affects all Rust-building jobs across the entire CI infrastructure. Jobs will continue to cache Cargo's registry of downloaded dependencies but will no longer cache compiled artifacts in the target directory. This should reduce cache storage requirements while maintaining build efficiency through SCCache (which remains enabled).

Pipeline Comparison

• #1 Pipeline 2197858950 This MR
• #2 Pipeline 2197466180

The difference shows how the duration of the job is this MR is faster/slower than the duration of the job in the second pipeline Checkmark is green ✅ if the job in this MR is faster or no slower than 60 seconds

Job Name	#1	#2	Diff
build-layer1-profiling	4m 28s	7m 40s	✅ -192s
oc.build:static-x86_64-linux-binaries	6m 5s	8m 38s	✅ -153s
oc.build_amd64-extra-dev	5m 52s	7m 14s	✅ -81s
oc.build_kernels	3m 42s	11m 43s	✅ -481s
oc.build_x86_64-released	3m 28s	6m 24s	✅ -176s