fix mzi with new routing

[joamatab]

• move cp2 in mzi and mzm to have enough space for 2 straights
• better error messages when vias do not fit in via_stacks

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 1.19%.

Quality metrics	Before	After	Change
Complexity	12.04 🙂	12.82 🙂	0.78 👎
Method Length	167.70 😞	173.11 😞	5.41 👎
Working memory	19.83 ⛔	20.44 ⛔	0.61 👎
Quality	37.63% 😞	36.44% 😞	-1.19% 👎

Other metrics	Before	After	Change
Lines	1169	1194	25

Changed files	Quality Before	Quality After	Quality Change
gdsfactory/components/mzi.py	28.97% 😞	28.50% 😞	-0.47% 👎
gdsfactory/components/mzm.py	33.97% 😞	33.84% 😞	-0.13% 👎
gdsfactory/components/via_stack.py	31.07% 😞	29.14% 😞	-1.93% 👎
gdsfactory/components/via_stack_slot.py	42.86% 😞	39.84% 😞	-3.02% 👎
gdsfactory/components/via_stack_with_offset.py	34.78% 😞	34.81% 😞	0.03% 👍
tests/test_import_gds_with_hierarchy.py	90.07% ⭐	90.07% ⭐	0.00%

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
gdsfactory/components/via_stack.py	via_stack	27 😞	520 ⛔	25 ⛔	13.33% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
gdsfactory/components/via_stack.py	via_stack_circular	26 😞	457 ⛔	17 ⛔	18.75% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
gdsfactory/components/mzi.py	mzi	13 🙂	614 ⛔	35 ⛔	21.51% ⛔	Try splitting into smaller methods. Extract out complex expressions
gdsfactory/components/via_stack_with_offset.py	via_stack_with_offset	12 🙂	379 ⛔	22 ⛔	26.49% 😞	Try splitting into smaller methods. Extract out complex expressions
gdsfactory/components/via_stack.py	via_stack_from_rules	14 🙂	390 ⛔	18 ⛔	27.11% 😞	Try splitting into smaller methods. Extract out complex expressions

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