feat: migrate build pipeline from tsc to tsdown

[chybisov]

Migrate build pipeline from tsc to tsdown

Closes EMB-317

TL;DR

Replace tsc --build with tsdown (powered by Rolldown/OXC in Rust) across all 5 SDK packages. Build time drops from ~13s to ~650ms (~20x faster).

DESCRIPTION

Before vs After

Metric	Before (tsc)	After (tsdown)	Improvement
Full build time	~13s	~650ms	~20x faster
Build passes per package	3 serial (CJS, ESM, types)	2 parallel (ESM+DTS, CJS)	Fewer passes
Package parallelism	SDK first, then 4 providers	All 5 fully parallel	No dependency ordering
Type checking	Coupled with build	Separate check:types step	Build never fails on type errors
Per-package (sdk)	~8s	~650ms	~12x faster
Per-package (provider)	~3s	~450ms	~7x faster

What changed

Root:

• Added tsdown as root devDependency
• Added isolatedDeclarations: true to root tsconfig (enables OXC-powered .d.ts generation)
• Simplified root build script to run all packages in parallel (no SDK-first ordering needed)
• Added scripts/build.js — wraps tsdown with per-package timing output

Per package (5 packages):

• Created tsdown.config.ts with ESM+DTS and CJS configs (ESM-only for sui)
• Replaced build:cjs / build:esm / build:types / build:clean with single tsdown call
• .d.ts files now live alongside ESM in dist/esm/ (no separate dist/types/)
• Updated types/typings/exports fields to point to dist/esm/index.d.ts
• watch updated to tsdown --watch
• check:types remains tsc --noEmit (no faster alternative exists yet)

Source files (~30 files):

• Added explicit return type annotations to all exported functions/constants (required by isolatedDeclarations)
• parseAbi results in abi.ts typed as Abi (viem's narrow generics incompatible with isolated declarations); downstream multicall results use as casts
• Removed dead return this from HTTPError.buildAdditionalDetails
• Fixed pre-existing TS2339 in parseEthereumErrors.ts

Why tsdown?

• Rust-powered: Uses Rolldown (Rust bundler) + OXC (Rust TypeScript toolchain) instead of the JavaScript-based tsc
• Parallel by design: ESM, CJS, and DTS builds run concurrently within each package
• isolatedDeclarations: Each file's .d.ts is generated independently without cross-file type resolution, enabling massive parallelism
• Drop-in: Output is semantically equivalent to tsc — same file structure, same module format, same declaration files

STEPS TO TEST

# Clean build
pnpm clean && pnpm build

# Verify outputs exist
ls packages/sdk/dist/esm/index.js packages/sdk/dist/cjs/index.js packages/sdk/dist/esm/index.d.ts

# Type checking (separate from build)
pnpm check:types

# Lint
pnpm check

# Tests
pnpm test:unit

EXPECTED RESULTS

• All 5 packages build successfully with timing output
• dist/esm/ contains .js, .js.map, .d.ts, .d.ts.map files
• dist/cjs/ contains .js, .js.map files (not for sui)
• All 284 unit tests pass
• pnpm check (biome) passes
• pnpm check:types passes

CHECKLIST

• Performed a self-review of my code
• Added comments to the code for better readability
• Added tests that cover the new functionality
• Made sure that existing tests are still passing.

[effie-ms]

SDK provider packages rely on core SDK package - shouldn't we still build core SDK first, or it's handled anyhow differently now?