Batch transaction inserts when building a block

[JamesHinshelwood]

Benchmark with this PR + #1942

produce-full/produce-full
                        time:   [1.6839 s 1.7362 s 1.7660 s]
                        thrpt:  [0.5662  elem/s 0.5760  elem/s 0.5938  elem/s]
                 change:
                        time:   [-55.243% -52.889% -50.495%] (p = 0.00 < 0.05)
                        thrpt:  [+102.00% +112.26% +123.43%]
                        Performance has improved.

Before:

After: