Fix/260 263 get oracle and player address tests

[maztah1]

closes #260
closes #263

Summary

Changes

get_oracle getter (fix #260)

• Added get_oracle(env: Env) -> Result<Address, Error> to EscrowContract
• Reads DataKey::Oracle from instance storage, consistent with the existing get_admin pattern
• Allows frontends and integrators to verify the trusted oracle without reading raw storage

Tests (fix #263 + #260)

• test_get_oracle_returns_initialized_address — asserts get_oracle returns the address passed to
  initialize
• test_get_match_returns_correct_players — asserts get_match returns the correct player1 and
  player2 addresses after match creation

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