Closes AC-1588. Holds global network values in-memory in a variable.

- Creates `internal/core.GlobalValues` type that is responsible for loading and storing network global value accounts.
- Changes marshalling for network global value accounts from JSON to binary.
- Adds an active and pending global values variable to the executor to track the current, active global values and pending changes.
- Adds logic to `internal/block.Executor.ProcessTransaction` to update the pending global values when the relevant account is changed.
- Adds additional validation to ensure it is impossible to update a network global value account to an invalid state.
- Enforces write-to-state for network global value account.
- Removes oracle from the ledger (use global values instead).
- Removes oracle from the directory anchor (updated via Updates instead).
- Updates executors to use the active global values instead of parsing data entries.
- Adds global values to API `describe` method
## Review Checklist

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- [x] The merge request title is in the format `<change type>(<change scope>): <short description> [<task id>]`
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- [x] The description includes `Closes <jira task ID>` (or rarely `Updates <jira task ID>`)
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## Merge Checklist

- [ ] CI is passing
- [ ] Merge conflicts are resolved
- [ ] All discussions are resolved

Related to AC-1588