test: add integration tests for `Pausable` plugins

[mooori]

Previously Pausable was tested by unit tests via near_sdk::testing_env, which mocks the chain.

The new integration tests compile the contract in near-plugins/tests/contracts/pausable, deploy it on chain via near workspaces and send transactions to it.

This is a step towards having only one contract for the Pausable plugin which is used for tests and serves as documentation resp. example, as laid out in #48. In a follow up PR I’ll clean up duplicate example contracts.

Other changes: refactor near-plugins/tests/common

• Removed superfluous types that complicated the code.
• Generalized helper functions to be used in tests of multiple plugins. Prior only AccessControllable was tested via integration tests.

[mooori]

CI is green and I've double checked that there are no more open TODOs related to this PR, so merging now.