feat(test):add tests for different date matcher scenarios in pact_ffi

[pulak777]

Tests for different date matcher scenarios (applicable for datetime/time as well) -

1. when pact:generator:type is provided in the body matcher, mock server returns current time (Local::now()) in the provided format
2. when not provided, mock server returns the specified value

Context - Currently when using pact-js v3 matcher type date and time, mock-server returns current date/time while it's expected to return the example date/time. The issue is not originating from here (will create a seperate pr for that in pact-js), but these additional tests might worth having.

[rholshausen]

There is a compile error with the tests:

error[E0433]: failed to resolve: use of undeclared type `Local`
    --> pact_ffi/tests/tests.rs:2216:24
     |
2216 |             let date = Local::now().format("%Y-%m-%d").to_string();
     |                        ^^^^^ use of undeclared type `Local`
     |
help: consider importing this struct
     |
1    + use chrono::Local;
     |

[pulak777]

oops! must have removed the import while reverting lint changes