[EPIC] too many memory allocations in tx execution

[yihuang]

Proposal: reduce memory allocations in tx execution

Current behavior:

When benchmark parallel EVM execution, memory allocation, and GC seem becoming a bottleneck.

And there are indeed many unnecessary allocations in both SDK and ethermint

Desired behavior:

Pick some low hanging fruits first:

• big int and legacy decimals
• unnecessary conversions between different representations (protobuf <-> go-ethereum).

Use case: [Why is this important (helps with prioritizing requests)]

Requests may be closed if we're not actively planning to work on them.

Tracking

• Problem: params not cached in object store #454
• Problem: inefficient transaction format #471
• avoid gas kv construction, we don't need gaskv in eth tx execution
• Problem: common parameters not cached #469
• reduce duplicated GetAccount calls
• reduce big.Int copy during bank operations