Remove account_id parameter from IndexerViewClient methods

[ayushsingh82]

Summary

• IndexerViewClient is always accessed through IndexerState, which already holds mpc_contract_id — every method taking it as a parameter was passing the same redundant value at every call site (there was already a TODO(#1514) in the code noting this)
• IndexerViewClient now stores its own copy of mpc_contract_id, set once in IndexerState::new
• Removed the parameter from all 12 methods on IndexerViewClient (get_pending_request, get_pending_ckd_request, get_pending_verify_foreign_tx_request, get_participant_attestation, get_supported_chains, get_foreign_chains_configs, get_available_chains, get_allowed_foreign_chain_providers, get_mpc_contract_state_dto, get_mpc_allowed_image_hashes, get_mpc_allowed_launcher_compose_hashes, get_mpc_tee_accounts, get_mpc_migration_info) and the private get_mpc_state helper
• Updated all call sites in tx_sender.rs, tee.rs (including the generic monitor_allowed_hashes fetcher, whose Fetcher bound dropped its AccountId argument), participants.rs, foreign_chain.rs, and migrations.rs
• IndexerState::mpc_contract_id itself is unchanged — it's still needed for building outgoing transactions, unrelated to IndexerViewClient

Closes #1514

Verification

• cargo check -p mpc-node --all-features: clean
• cargo clippy -p mpc-node --all-targets --all-features -- -D warnings: clean (type-checks test code too)
• cargo fmt -- --check: clean
• Wasn't able to complete a full cargo test link+run locally (linking mpc-node's test binary, which statically pulls in nearcore/near-client/etc., needs more disk than my local environment has available) — cargo check/clippy --all-targets already confirm the test code (including #[cfg(test)] modules) type-checks correctly under the new signatures. Happy to fix up anything CI's actual test run surfaces.

Test plan

• CI clippy job passes
• CI test suite passes