chore: enable std feature when mocks is enabled

`mocks` feature results in use of `Timestamp::now` which is only
defined when `std` feature is enabled.  Make `std` implied by `mocks`.

crates/ibc/Cargo.toml

@@ -21,7 +21,7 @@ default = ["std"]
 std = [
     "ibc-proto/std",
     "ics23/std",
-    "serde/std",    
+    "serde/std",
     "tracing/std",
     "prost/std",
     "bytes/std",
@@ -46,7 +46,7 @@ schema = ["dep:schemars", "serde", "std"]
 
 # This feature grants access to development-time mocking libraries, such as `MockContext` or `MockHeader`.
 # Depends on the `testgen` suite for generating Tendermint light blocks.
-mocks = ["tendermint-testgen", "tendermint/clock", "parking_lot", "typed-builder"]
+mocks = ["tendermint-testgen", "tendermint/clock", "parking_lot", "typed-builder", "std"]
 
 [dependencies]
 # Proto definitions for all IBC-related interfaces, e.g., connections or channels.