refactor(common): move scanner/heal contracts into dedicated crates (#6615)

refactor(common): move scanner/heal domain contracts into dedicated crates

crates/common carried ~5.6K lines of scanner/heal domain code (metrics.rs,
heal_channel.rs, last_minute.rs) parked there to break dependency cycles;
every scanner type change recompiled all 11 rustfs-common dependents.

Pure move, zero renames, zero shape changes (backlog#1843):

- New crate rustfs-heal-contracts receives heal_channel.
- New crate rustfs-scanner-contracts receives metrics, last_minute, and the
  GLOBAL_INIT_TIME trio (metrics::report() reads it as the current-cycle
  fallback, so it must live below the shim to avoid a dependency cycle).
- rustfs-common re-exports everything at the old paths as a transitional
  shim; consumers migrate crate by crate, then the shims are deleted.

crates/scanner-contracts/Cargo.toml

@@ -0,0 +1,45 @@
+# Copyright 2024 RustFS Team
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+[package]
+name = "rustfs-scanner-contracts"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+rust-version.workspace = true
+homepage.workspace = true
+description = "Scanner metrics and lifecycle-cycle contracts shared by the scanner, storage engine, and observability layers."
+keywords = ["scanner", "contracts", "metrics", "rustfs", "Minio"]
+categories = ["web-programming", "development-tools", "data-structures"]
+
+[lints]
+workspace = true
+
+[dependencies]
+chrono = { workspace = true, features = ["serde"] }
+jiff = { workspace = true, features = ["serde"] }
+metrics = { workspace = true }
+rmp-serde = { workspace = true }
+rustfs-heal-contracts = { workspace = true }
+serde = { workspace = true, features = ["derive"] }
+tokio = { workspace = true, features = ["sync"] }
+
+[dev-dependencies]
+serde_json = { workspace = true }
+tokio = { workspace = true, features = ["macros", "rt-multi-thread"] }
+uuid = { workspace = true, features = ["v4"] }
+
+[lib]
+doctest = false