Replace C-style libpq parameter arrays with std::array in Postgres stores

[MisterVVP]

Motivation

• Fix clang-tidy modernize-avoid-c-arrays errors caused by C-style parameter arrays passed to PQexecParams in the PostgreSQL store implementation.
• Make parameter handling explicit and safer by using std::array and calling .data() when interoperating with libpq APIs.

Description

• Added #include <array> to postgres_task_store.cpp and postgres_notification_store.cpp and introduced constexpr parameter counts for affected queries.
• Replaced const char* ...[], int ...[], and similar C-style arrays with std::array<const char*, N> / std::array<int, N> in task upsert, select-for-update, get, and other query paths in src/server/stores/postgres_task_store.cpp.
• Applied the same change to push notification store upsert, lookup/existence check, count, list, and delete paths in src/server/stores/postgres_notification_store.cpp, and passed .data() into PQexecParams calls.
• Kept semantics unchanged (same parameter ordering, lengths/formats, and PQexecParams usage) while eliminating C-style array declarations.