iterate dbNets rather than sta nets when fetching parasitics

[AcKoucher]

Requires #4405.

The script currently iterate sta nets and uses sta_to_db_net which will return nullptr for module net. That caused the script to crash when trying to retrieve the type of that net.

With the changes here we should be properly considering the parasitics of all dbNets when fetching and preventing the crash.

[gemini-code-assist]

Code Review

This pull request introduces a helper function find_flat_db_net in flow/util/write_rc_helper.tcl to resolve flat database nets and refactors several functions to use it. It also adds deduplication logic to prevent processing the same flat net multiple times. The feedback highlights a potential runtime error in find_flat_db_net if sta::sta_to_db_mod_net returns "NULL", and suggests adding a check before calling findRelatedNet.

[openroad-ci]

🔍 QoR check

Metrics reflect the PR merge build — i.e. what will land on the target branch. Advisory — results are log-only and do not affect build status. The authoritative QoR gate remains the local rules-file check.

Commit 790de4b · Jenkins build #4 · Baseline: build

61 design(s) checked — 0 with regression(s), 7 without a comparable baseline.

Design	Variant	Verdict	local vs inline	passed / failed / missing
asap7/aes	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/aes-block	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/aes-mbff	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/aes_lvt	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/cva6	base	✅ pass	✅ MATCH	12 / 0 / 0
asap7/ethmac	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/ethmac_lvt	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/gcd	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/gcd-ccs	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/ibex	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/jpeg	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/jpeg_lvt	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/mock-alu	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/mock-cpu	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/riscv32i	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/riscv32i-mock-sram	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/swerv_wrapper	base	✅ pass	✅ MATCH	23 / 0 / 0
asap7/uart	base	✅ pass	✅ MATCH	23 / 0 / 0
gf180/aes	base	✅ pass	✅ MATCH	23 / 0 / 0
gf180/aes-hybrid	base	✅ pass	✅ MATCH	23 / 0 / 0
gf180/ibex	base	✅ pass	✅ MATCH	23 / 0 / 0
gf180/jpeg	base	✅ pass	✅ MATCH	23 / 0 / 0
gf180/riscv32i	base	✅ pass	✅ MATCH	23 / 0 / 0
gf180/uart-blocks	base	✅ pass	✅ MATCH	23 / 0 / 0
gt2n/aes	base	➖ inconclusive	➖ N/A	0 / 0 / 457
gt2n/gcd	base	➖ inconclusive	➖ N/A	0 / 0 / 451
gt2n/jpeg	base	➖ inconclusive	➖ N/A	0 / 0 / 456
ihp-sg13g2/aes	base	✅ pass	✅ MATCH	23 / 0 / 0
ihp-sg13g2/gcd	base	✅ pass	✅ MATCH	23 / 0 / 0
ihp-sg13g2/i2c-gpio-expander	base	✅ pass	✅ MATCH	23 / 0 / 0
ihp-sg13g2/ibex	base	✅ pass	✅ MATCH	23 / 0 / 0
ihp-sg13g2/jpeg	base	✅ pass	✅ MATCH	23 / 0 / 0
ihp-sg13g2/riscv32i	base	✅ pass	✅ MATCH	23 / 0 / 0
ihp-sg13g2/spi	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/aes	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/ariane133	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/ariane136	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/black_parrot	—	➖ inconclusive	➖ N/A	no reports directory — flow produced no output
nangate45/bp_be_top	—	➖ inconclusive	➖ N/A	no reports directory — flow produced no output
nangate45/bp_fe_top	—	➖ inconclusive	➖ N/A	no reports directory — flow produced no output
nangate45/bp_multi_top	—	➖ inconclusive	➖ N/A	no reports directory — flow produced no output
nangate45/dynamic_node	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/gcd	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/ibex	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/jpeg	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/mempool_group	base	✅ pass	✅ MATCH	12 / 0 / 0
nangate45/swerv	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/swerv_wrapper	base	✅ pass	✅ MATCH	23 / 0 / 0
nangate45/tinyRocket	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/aes	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/chameleon	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/gcd	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/ibex	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/jpeg	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/microwatt	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hd/riscv32i	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hs/aes	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hs/gcd	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hs/ibex	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hs/jpeg	base	✅ pass	✅ MATCH	23 / 0 / 0
sky130hs/riscv32i	base	✅ pass	✅ MATCH	23 / 0 / 0