Optimize get_evm_confirmed_full_blocks (storage-bigtable); create and test version for headers only

[dj8yfo]

Problem

Tested

    pub async fn get_evm_confirmed_full_blocks(
        &self,
        first_block: evm_state::BlockNum,
        last_block: evm_state::BlockNum,
    ) -> Result<Vec<evm_state::Block>> {

it works reliably;
add version of the same, returning BlockHeader-s instead of Block-s

Proposed Solution