StateDB intermediate state reset when opening DB to force getting always last
Checkpoint at last BatchNum, avoiding inconsistent intermediate state.

Update log package with fields & file log, and update constants in the
repository code to be MixedCase.

resolves #91, resolves #92, resolves #95

- gofmt - Gofmt checks whether code was gofmt-ed. By default this tool runs
  with -s option to check for code simplification
- goimports - Goimports does everything that gofmt does. Additionally it checks
  unused imports
- golint - Golint differs from gofmt. Gofmt reformats Go source code, whereas
  golint prints out style mistakes
    - checks the uncommented exported functions & types

Update the code to fix the lint checks.

Add linter checks to GHA & Fix code to pass lints.
The linters added are:
- whitespace: Tool for detection of leading and trailing whitespace
- gosec: Inspects source code for security problems
- gci: Gci control golang package import order and make it always deterministic
- misspell: Finds commonly misspelled English words in comments
- gomnd: An analyzer to detect magic numbers

The file utils/utils.go is excluded from the checks of gomnd, as uses magic numbers through the code

Update StateDB to new & ExitInfo struct & BatchNum
Also a small fix at txselector & log packages

Add StateDB tx processor tests using tx test generators:
- update statedb/ tx processors
- add statedb tx processors tests

- Update GHA lint.yml increasing timeout time to avoid GHA Lint errors
- Update common.BatchNum & common.Idx & common.Nonce usage in StateDB
- Add abstraction method of processTxs to StateDB
    - Which will be used by Synchronizer & BatchBuilder

Previously as the txprocessor.go methods were specific for the BatchBuilder,
the MTCreateAccount & CreateAccount and MTUpdateAccount & UpdateAccount were
also designed to be used by BatchBuilder and TxSelector depending on the
MerkleTree usage calling one kind of method or anotherone.

But now that this methods are being called directly by the StateDB (through the
methods in txprocessors.go), to allow also the methods usage from the
Synchronizer, there can not be the MT and no-MT methods separated, so this
commit unifies MTCreateAccount with CreateAccount, and MTUpdateAccount with
UpdateAccount, which internally will update the MerkleTree depending if the
specific StateDB in usage has the MerkleTree defined or not.

Migrate TxProcessors from BatchBuilder to StateDB in order to be used by
BatchBuilder & Synchronizer

Co-authored-by: Eduard S. <eduard@iden3.io>