test: add share-conservation property harness via proptest

[AdeMi20]

I have created the property-based test harness in src/test_share_conservation_prop.rs which leverages the existing proptest_helpers.rs strategies to generate randomized sequences of contract operations. The harness tracks the active offerings and all registered holders, and iteratively executes the randomly generated operations (like set_holder_share and register_offering), strictly asserting that the sum of holder shares never exceeds 10,000 basis points after each successful step. Additionally, to ensure the test suite compiles and can successfully run the 10,000 required sequences in CI, I had to resolve several pre-existing compilation errors in src/lib.rs. This included migrating several new variants (such as SnapshotFinalized and MinRevenueThreshold) from the DataKey enum to DataKey2 to bypass the Soroban XDR limit of 50 variants, fixing duplicate error codes in RevoraError, and explicitly defining a missing PauseState enum.

Close #464

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