feat(reputation-registry): gate get_score behind pause circuit breaker

[fridaypetra55-afk]

Summary

• record_activity and the other mutating entry points already checked pause::when_not_paused, but get_score did not — so a paused contract (e.g. after a scoring bug is discovered) would still happily serve scores while it's under investigation.
• get_score now returns Result<MoiScore, ReputationError> and rejects with ContractPaused when paused, consistent with every other entry point in the contract. The generated Soroban client keeps the ergonomic client.get_score(...) panicking-on-error call site working unchanged; client.try_get_score(...) is used where the paused error needs to be observed.
• Added a test_pause_blocks_get_score test mirroring the existing test_pause_blocks_record pattern.

Note on pre-existing breakage (unrelated to this change)

While validating this fix I found reputation-registry's own test suite does not currently compile on master, for reasons unrelated to this issue:

• lib.rs never re-exports types::* (e.g. crate::MoiScore), which test.rs imports directly.
• test.rs calls client.record(...) / client.try_record(...), but the contract only exposes record_activity.
• test.rs uses Events::last() as an iterator, which isn't supported by the pinned soroban-sdk version's testutils API.
• reputation-registry/Cargo.toml was also missing the testutils dev-dependency that circle/Cargo.toml has, so the package couldn't even attempt to build its tests — I've added that here since it's needed for this package to build its own test suite at all.

This is likely why it was never caught: the CI workflow at .github/workflows/*.yml triggers on branches: ["main"], but the repo's default branch is master, so cargo test --workspace / clippy have not actually been running in CI. I did not attempt to fix the pre-existing record/export/Events issues here since they're out of scope for #118 — happy to file that as a separate issue if useful. I did verify cargo build -p reputation-registry (the actual contract lib, non-test) compiles cleanly with this change.

Closes #118

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