Rename Predict oracle cap to writer cap

[pei-mysten]

Summary

• Rename MarketOracleCap to MarketOracleWriterCap across Predict sources, tests, and gas benchmark setup.
• Rename the associated error/auth helpers and authorized-cap storage to use writer-cap terminology.
• Keep behavior unchanged: the renamed cap still gates price, SVI, settlement, compaction, and oracle bounds paths in this PR.

Naming

WriterCap avoids confusion with the package-level AdminCap while describing the capability precisely: it authorizes writes to oracle data/config.

Stack

• This is PR 1 of 2.
• Follow-up PR Introduce Predict oracle lifecycle cap #1068 introduces MarketOracleLifecycleCap and moves lifecycle-only operations off the writer cap.

Tests

• sui move test -p packages/predict -i 100000000 oracle_cap_tests
• sui move test -p packages/predict -i 100000000 market_oracle_getters_tests
• sui move test -p packages/predict -i 100000000 market_oracle_update_prices_tests
• sui move test -p packages/predict -i 100000000 market_oracle_set_bounds_tests
• npx --yes --package @mysten/prettier-plugin-move prettier-move -c $PWD/packages/predict/**/*.move
• git diff --check