CelestaUnit improvements

[inponomarev]

Overview

1. Clean up before each test, not after each test.
2. Reset sequences.
3. Reuse CallContext from @BeforeEach call.
4. Parameterized @CelestaTest annotation.

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Checklist

• Change is covered by automated tests.
• JavaDoc / User Guide is updated.
• CI builds pass.
• PR is tagged.