"whitelisting" mechanism (list of files - stored in DB) - which
protecting us from downloading new files after upgrade/downgrade was
broken. And seems it became over-complicated with time.
I replacing it by 1 persistent flag inside downloader:
"prohibit_new_downloads.lock"
Erigon will turn downloader into this mode after
downloading/verification of first snapshots.
```
//Corner cases:
// - Erigon generated file X with hash H1. User upgraded Erigon. New version has preverified file X with hash H2. Must ignore H2 (don't send to Downloader)
// - Erigon "download once": means restart/upgrade/downgrade must not download files (and will be fast)
// - After "download once" - Erigon will produce and seed new files
```
------
`downloader --seedbox` is never "prohibit new downloads"
This introduces _experimental_ RPC daemon run by embedded Silkworm
library. Same notes as in PR #8353 apply here plus the following ones:
- activated if `http` command-line option is enabled and `silkworm.path`
option is present, nothing more is required (i.e. currently, both block
execution and RPC daemon run by Silkworm when specifying
`silkworm.path`, just to keep things as simple as possible)
- only Execution API endpoints are implemented by Silkworm RPCDaemon,
whilst Engine API endpoints are still served by Erigon RPCDaemon
- some features are still missing, in particular:
- state change notification handling
- custom JSON RPC settings (i.e. Erigon RPC settings are not passed to
Silkworm yet)
This introduces _experimental_ block execution run by embedded Silkworm
API library:
- new command-line option `silkworm.path` to enable the feature by
specifying the path to the Silkworm library
- the Silkworm API shared library is dynamically loaded on-demand
- currently requires to build Silkworm library on the target machine
- available only on Linux at the moment: macOS has issue with [stack
size](https://github.com/golang/go/issues/28024) and Windows would
require [TDM-GCC-64](https://jmeubank.github.io/tdm-gcc/), both need
dedicated effort for an assessment
