v2.18.0

ModelingToolkitStandardLibrary v2.18.0

Diff since v2.17.0

Merged pull requests:

• Add capacitor initial voltage to README.md example (#341) (@jaakkor2)
• build(deps): bump codecov/codecov-action from 4 to 5 (#342) (@dependabot[bot])
• Add diode component (#343) (@langestefan)
• test: fix thermal piston test (#344) (@AayushSabharwal)
• Add variable resistor component (#346) (@langestefan)
• fix: change HeatPort to allow changing the guess (#347) (@avinashresearch1)