feat: add bundle size checks and update size limits for all exports

[ChukwuemekaP1]

Summary

Implemented per-entry bundle-size budgets and CI enforcement for all public package exports.

Changes

• Added size-limit configurations for EVM, Solana, CKB, Vault, and the root entry.
• Set bundle-size budgets based on the current baseline with 15% headroom.
• Updated BUNDLE_SIZE.md with the actual bundle sizes, budgets, and usage commands.
• Updated CI so pnpm size runs for PRs that modify src/.
• Verified the size-limit gate correctly fails when a bundle exceeds its configured budget.

Closes #180

All public package entries now have documented bundle-size limits, preventing unintended bundle growth from being merged.

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[truthixify]

Merged. Real measured baselines with a documented +15 percent rule, both ESM and CJS per entry, and the paths-filter so it only runs when src/** changes.

Special credit for the Stellar note: you found that the old 20 KB budget had never actually been measured (the baseline was a TBD placeholder), said so plainly, and re-baselined it under the same rule as everything else rather than quietly bumping the number. That is the right way to handle a budget that was never real. @ChukwuemekaP1