fix(bug): address `?at` bug and `endingOffset` conditionals (#824)

* fix: current auction endingOffset bug

* fix: header bug

* update tests to accurately test the updates

* add vrfDelay to endingOffset

* refactor logic to make it cleaner

* Update src/services/paras/ParasService.ts

Co-authored-by: Zeke Mostov <[email protected]>

* Update src/services/paras/ParasService.ts

Co-authored-by: Zeke Mostov <[email protected]>

* remove vrfDelay from offset calculation

* update docs with vrfDelay info

* add tests for startPeriod, endPeriod and vrfDelay

* inline docs

* fix some grumbles for vrfDelay, and endPeriod sample

* Update src/services/paras/ParasService.ts

* Update docs

* Update src/services/paras/ParasService.ts

Co-authored-by: James Wilson <[email protected]>

* fix naming in test

* set the vrfDelay test to use the finishEnd block

* update docs

Co-authored-by: Zeke Mostov <[email protected]>
Co-authored-by: James Wilson <[email protected]>