fix: remove OpenSSL dependency by migrating isahc to reqwest (rustls-tls)

This commit fixes CI failures caused by curl-sys requiring OpenSSL 3.0.0+
which is not available in the CI container image (Debian bullseye).

Changes:
- Replace isahc with reqwest (rustls-tls feature) in relay-utils
- Remove isahc from workspace dependencies
- Update reqwest to use rustls-tls and json features
- Update Cargo.lock (removes curl, curl-sys, isahc, openssl-sys, native-tls)

Benefits:
- Pure Rust TLS implementation (no OpenSSL dependency)
- More portable across different Linux distributions
- Eliminates C compilation requirements for TLS
- Better security (memory-safe TLS implementation)

Affected workflows:
- Checks / cargo-clippy
- Checks / check-try-runtime
- Docs / test-doc, build-rustdoc
- Build and push images
- tests linux stable
- tests misc

Cargo.toml

@@ -850,7 +850,7 @@ integer-sqrt = { version = "0.1.2" }
 ip_network = { version = "0.4.1" }
 is-terminal = { version = "0.4.9" }
 is_executable = { version = "1.0.1" }
-isahc = { version = "1.2" }
+# isahc removed - replaced with reqwest (rustls-tls) to eliminate OpenSSL dependency
 itertools = { version = "0.11" }
 jobserver = { version = "0.1.26" }
 js-sys = { version = "0.3.70" }
@@ -1448,7 +1448,8 @@ regex = { version = "1.10.2" }
 relay-bizinikiwi-client = { version = "0.1.0", path = "pezbridges/relays/client-bizinikiwi" }
 relay-utils = { version = "0.1.0", path = "pezbridges/relays/utils" }
 remote-externalities = { path = "bizinikiwi/utils/pezframe/remote-externalities", version = "0.35.0", default-features = false, package = "pezframe-remote-externalities" }
-reqwest = { version = "0.12.9" }
+# Using rustls-tls for pure Rust TLS - no OpenSSL dependency
+reqwest = { version = "0.12.9", default-features = false, features = ["rustls-tls", "json"] }
 revm = { version = "27.0.2", default-features = false }
 ripemd = { version = "0.1.3", default-features = false }
 rlp = { version = "0.6.1", default-features = false }