analyzer/runtime: Deposit/Withdraw txs: make "to" explicit

[mitjat]

This PR:

• makes sure the to field of a tx (in the DB and the API) is always populated
• adds an initial unit(ish) test for the runtime analyzer, with the ambition that more will follow in future PRs

Background:
For txs with method consensus.Deposit or consensus.Withdraw, the to field in the body is optional; when omitted, the implied semantics are that the deposit/withdrawal is happening to the account of the tx sender.

Nexus's /transactions endpoint lists txs with their raw body (where we don't want to inject the implicit to), but also with an additional to field that we extract from txs regardless of the method. This PR makes it so that this field is always filled, even if to in the tx body is missing.

Testing:

• Manual. I indexed round 316043 from pontusx that is known to contain a tx with an implicit to, and verified the API response.
• The included test.
• The regression e2e range unfortunately does not include any deposits with an implicit to, so the change is not visible there :(

[pro-wh]

is this started from another branch?

[pro-wh]

lg, cool tests

[mitjat]

I cannot fully decide if this is the right abstraction level. We could narrow the scope of tests and analyze the internal variables that the runtime analyzer populates during analysis, and then uses them to generate DB statements. The upside of that would be a more focused test. The downside would be having to treat the analyzer a lot more as a white box. Another downside is that it would make it harder to port these tests to consensus: The consensus analyzer doesn't have that convenient intermediate in-memory representation, it produces DB statements more directly from node data.
So I decide to go with this, and tweak/refactor it later if needed. 🤷

[mitjat]

Unrelated changes; I just found the old wording slightly misleading when debugging pontusx.