refactor(pinger): replace hashlru with standard HashMap and manual TTL cleanup

Remove the hashlru dependency to reduce bloat, replacing it with a Mutex-wrapped HashMap and manual entry expiration logic.

Cargo.toml

@@ -29,7 +29,6 @@ rust-uci = { git = "https://github.com/namib-project/rust-uci.git", rev = "71ea7
 thiserror = "2.0"
 libc = "0.2"
 flume = { version = "0.12.0",  default-features = false, features = ["eventual-fairness", "select"] }
-hashlru = { version = "0.11.1", default-features = false }
 
 [dependencies.log]
 features = ["std"]