Sabaun Taraki

This PR refactors mailbox logic in the `gtest` fixing some error inconsistencies with the runtime and, mainly, adding `gear_common` version of `Mailbox`.

### Problem to Solve By default max value is just used and all messages (original and generated during the execution of the original) are being run as they were all...

### Proposal This is more about refactoring, but not a bug. Related to this PR https://github.com/gear-tech/gear/pull/3901. It's impossible to make a "transactional" implementation of the `gr_read` in current design, so...

### Proposal We need to test every fallible, and _resources consuming_ (i.e., gas, reseravations, value and etc.) method, that it doesn't apply changes on these resources if error occurs Related...

Make it able to define `wasm-gen` config in `runtime-fuzzer` from caller side (i.e., fuzz target)

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### File Location(s) _No response_ ### Proposal Currently `runtime_fuzzer::generator::upload_program` uses `config` function with a "static" generation of the config for `wasm-gen`. So there's no possibility to set a custom config...

Resolves #4099 TODO: - [ ] use macro to avoid copy-paste in `EventsStreamProducer`

### Proposal Add check that re-instrumented code length is in the boundaries of the `Schedule` max code len.

refactor(gtest): improve API and docs

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- Rename `ActorMailbox` to `UserMailbox`, because there's no mailbox for programs - Rework logs concept: `Log`s (`Log` and `CoreLog`, `DecodedCoreLog`) were introduced in the beginning of the `gtest`. Being useful,...

### Problem to Solve @breathx: Transaction can't be considered to be unique only by checking it's existence in the storage.

ethexe: introduce tx pool error types

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This is mainly useful for RPC and validation: 1. RPC will send a response with a clear error message. 2. Some validation failures signalize that this error can be returned...