fix!: e2e tests are flaky due to slow app state processing

[lklimek]

Issue being fixed or feature implemented

TestApp_TxTooBig fails in GHA pipelines due to long execution time.
It is caused by JSON serialization within example kvstore application, which consumes significant amount of time and memory.

What was done?

1. Instead of running the test on each node one by one, broadcast txs to all nodes first, and then check results in separate loop.
2. Refactored kvstore to use streaming JSON serialization and deserialization when saving/restoring state.
3. Changed GenesisDoc.AppState to []byte
4. Updated e2e to use new format of initial app state
5. In e2e dashcore and rotate networks, decreased block size and evidence size to consume less resources during test

How Has This Been Tested?

GHA

Breaking Changes

Genesis doc AppState MUST be a base64-encoded bytes array, not JSON string.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[shumkov]

👍