feat: add root-level EditorConfig for contributor consistency

[faisalnugroho]

Summary

Adds .editorconfig to establish consistent coding styles across the monorepo.

Changes

• Added .editorconfig with rules for indentation, line endings, charset, trailing whitespace, and final newline
• Covers Python (4 spaces), JS/TS/JSON/YAML (2 spaces), Markdown (preserve trailing whitespace)

Motivation

Contributors use different editors with different default settings. An .editorconfig ensures consistent formatting regardless of editor, reducing style-related review noise.

Closes #2655

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[vercel]

@faisalnugroho is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[faisalnugroho]

Hi! Following up on this tooling PR. This PR adds an EditorConfig file for consistent formatting across different editors and contributors.

All CI checks pass (StepSecurity ✅). Would love to get your review when you have a moment. Thanks!

[faisalnugroho]

Hi! I'd love to get this PR reviewed when you have a moment. This PR addresses add root-level EditorConfig for contributor consistency. Happy to make any adjustments based on your feedback. Thank you!