Cardano Updates

Signed-off-by: William Hankins <[email protected]>

Signed-off-by: William Hankins <[email protected]>

Might still want a refactor into new_epoch() as per main
but there are issues around when SPOs are actually removed

Signed-off-by: William Hankins <[email protected]>

Need checking around SPOState end of epoch - retained my updated
version which does it in handle_tx_certs, may need refactoring
again with end_epoch() as in main

Also remove errors/warnings about missing SPOs (they can retire)
and VRF matches (they are OBFT nodes)

Epoch 211 treasury now matches again

refactor: Mithril fetcher to download intelligently

feat: REST Blockfrost module

- Modified the `should_skip_download` function to retrieve the download max age from the configuration instead of passing it as a parameter.
- Updated related tests to use the new configuration-based approach for determining download behavior.

- Implemented tests for saving and loading snapshot metadata.
- Added tests to verify the logic for skipping downloads based on snapshot age and availability.

- Introduced functions to load and save snapshot metadata as JSON.
- Implemented logic to skip downloading snapshots based on a configurable max age.
- add new `download-max-age` configuration variable for controlling snapshot download behavior.
- Added `chrono` dependency for date and time handling.

Signed-off-by: William Hankins <[email protected]>

Use 'mark' fees (epoch n-2 when entering epoch n) for calculating
treasury cut.

Still not convinced of this but it matches figures in DBSync!

Allows us to do things in this order:

- Monetary change (monetary expansion, treasury increase)
- Repay refunds and pay MIRs
- Capture snapshot
- Calculate rewards

However this still requires us to delay the fees by one epoch
to match DBSync numbers - unexplained!