Implement all FFI methods relating to `Pact`

[JP-Ellis]

Description

• Implement all missing methods for the Pact class. The scope of 'all' here relates to the methods exposed by the FFI which typically either: construct a Pact (returning a PactHandle); or, take a PactHandle as an argument and modify the underlying Pact
• Ensure all new methods are systematically unit-tested.

Has this been requested on Canny?

No

Motivation

Initial work implementing the Pact class was done as part of #410; however, the scope of the PR was limited to a MWE to ease with the review and ensure that the more substantive/foundational parts can be reviewed and the finer implementation details can kept separate.

Have you tried building it?

Continuation of prior work.

Self-service

• I'd be willing to contribute this feature to Pact Python myself.

[github-actions]

👋 Hi! The 'smartbear-supported' label has just been added to this issue, which will create an internal tracking ticket in PactFlow's Jira (PACT-1396). We will use this to prioritise and assign a team member to this task. All activity will be public on this ticket. For now, sit tight and we'll update this ticket once we have more information on the next steps.

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