Replace assertions with error macros

[comphead]

There are some places in Datafusion doing assertions which leads the application to crash. Its better to replace assertions with error wherever possible

Example: assert_eq! here to keep it consistent with other implementations of GroupsAccumulator. Eg. see here among others: https://github.com/apache/datafusion/blob/main/datafusion/physical-expr/src/aggregate/groups_accumulator/prim_op.rs?plain=1#L93

Originally posted by @lkt in https://github.com/apache/datafusion/pull/10149#discussion_r1579262396