* rpc: Make HTTP server timeout values configurable
* rpc: Remove flags for setting HTTP Timeouts, configuring via .toml is sufficient.
* rpc: Replace separate constants with a single default struct.
* rpc: Update HTTP Server Read and Write Timeouts to 30s.
* rpc: Remove redundant NewDefaultHTTPTimeouts function.
* rpc: document HTTPTimeouts.
* rpc: sanitize timeout values for library use