Call .onLoad during package loading

[Copilot]

loadfast was not calling .onLoad hooks (typically defined in zzz.R), unlike devtools::load_all() and normal R package loading. Packages relying on .onLoad for initialization (options, registrations, connections, etc.) would silently skip that setup.

Changes

• .loadfast.run_onload() helper — calls ns_env$.onLoad(dirname(abs_path), pkg_name) if defined, matching standard R argument convention; errors are downgraded to warnings
• Full load: .onLoad fires after exports are set and testthat is attached, but before attach() — matching standard R ordering (.onLoad before .onAttach)
• Incremental reload: .onLoad fires after changed files are re-sourced and pkg env is synced; skipped on the no-change short-circuit
• Tests (Stage 4l): verifies correct libname/pkgname arguments, suppression on no-change reload, and re-invocation on incremental reload

Example

# R/zzz.R
.onLoad <- function(libname, pkgname) {
  options(mypkg.timeout = 30L)
}

Previously load_fast() would ignore this; now it is called on every load that sources files.

[ak-finccam]

@felix-andreas-finccam Ich würde das hier dann mergen, richtig?

[felix-andreas-finccam]

hab's gemergt