Router Heap documentation update

[nedsels]

Two changes to Router Heap documentation:

1. Currently: u is protected and so doesn't appear in the documentation, but the descriptions of its accessors/mutators refer to it. Now: these functions' descriptions don't reference u and state explicitly what they do.
2. Currently: there are duplicate descriptions for public pure virtual functions inherited from HeapInterface and/or KAryHeap. Now: only HeapInterface has descriptions for its public members (its inherited classes do not have any additional public functions).

[vaughnbetz]

Thanks!
There's one spurious CI failure: a single reg test of small designs with OdinII has a QoR failure. Probably was introduced in some prior PR and needs a golden solution update. Merging this, but if it persists it would be good if you can update the checked in golden results for it.

vtr_reg_nightly_test1_odin/arithmetic_tasks/FIR_filters_frac...[Fail] 2024-06-28T17:21:45.4560546Z 17:21:45 | [Fail] 2024-06-28T17:21:45.4562104Z 17:21:45 | k6_frac_uripple_N8_22nm.xml/fir_nopipe_26.v/common setup_TNS relative value 1.5002228616457025 outside of range [0.5,1.4] and not equal to golden value: -782.997 2024-06-28T17:21:45.4564196Z 17:21:45 | vtr_reg_nightly_test1_odin/arithmetic_tasks/multless_consts...[Pass] 2024-06-28T17:21:45.4565543Z 17:21:45 | vtr_reg_nightly_test1_odin/arithmetic_tasks/open_cores...[Pass] 2024-06-28T17:21:45.4566654Z 17:21:45 | vtr_reg_nightly_test1_odin/arithmetic_tasks/open_cores_frac...[Pass] 2024-06-28T17:21:45.4567883Z 17:21:45 | regression_tests/vtr_reg_nightly_test1_odin/power_extended_arch_list...[Pass] 2024-06-28T17:21:45.4569127Z 17:21:45 | regression_tests/vtr_reg_nightly_test1_odin/power_extended_circuit_list...[Pass] 2024-06-28T17:21:45.4570176Z 17:21:45 | 2024-06-28T17:21:45.4571064Z 17:21:45 | Test 'vtr_reg_nightly_test1_odin' had 1 qor test failures