Validate network name in test config #34
Description
Summary
Add validation for the network field in the test configuration so invalid values are caught early instead of causing confusing runtime errors.
Background
There is a TODO in crates/test/src/config.rs (line 46) noting that network name validation should be implemented.
Current behavior
The [test.esplora] section accepts a network field. According to the README, valid values are: Liquid, LiquidTestnet, ElementsRegtest. Invalid or misspelled values may not be rejected until later, making debugging harder.
Proposed solution
Validate the network field when loading the config and return a clear error if the value is not one of the allowed options.
Files involved
crates/test/src/config.rs