chore(release): esplora-client v0.12.3

[oleonardolima]

It's a tracking issue for issues and PRs that should land in the next v0.12.3 release of esplora-client.

We are planning this v0.12.3 release from the release/0.12.x in order to have the deprecation warning of the methods that are planned to be removed in the next MAJOR release v0.13.0.

• feat(client): add get_block_infos and deprecate get_blocks #164
• chore(release): bump package to 0.12.3 #167

[luisschwab]

@oleonardolima missing #168