fix: force using simulated gas estimation

[amimart]

Purpose of Changes and their Description

Enforces the usage of estimated gas during tx simulation, the tx simulation is now systematic for that purpose and gas configuration related to the old behaviour has been removed (config files containing old fields won't cause any trouble).

This has been tested locally, with situations causing account sequence mismatches to ensure reliability over it.

Misc

• The tx is now signed only after simulation, as it is not required for it;

Are these changes tested and documented?

• If tested, please describe how. If not, why tests are not needed.
• If documented, please describe where. If not, describe why docs are not needed.
• Added to Unreleased section of CHANGELOG.md?

[xmariachi]

Approved, with a comment