transpile with tsdown instead of tsc

[dynst]

Lays the necessary groundwork for #1804

dist/ is the default output directory. https://tsdown.dev/options/output-directory

(Possibly blocked on #1816 to drop a use of node:crypto paulmillr/noble-hashes@c7ad207) Or not. Found a workaround.

yarn pack-web was failing in the stargate package because:

• @cosmjs/crypto was being bundled into the build/ directory, along with all its dependencies recursively;
• This was because it exists in "devDependencies" and not in "dependencies";
• This would be harmless (webpack is about to bundle all code+dependencies into 1 file anyway), but one of the recursive dependencies, @noble/hashes, has a particular file that varies in its resolution depending on the environment being node or not-node;
• This was being resolved at bundling-time, copying node-specific code (cryptoNode.js) into build/;
• Resolution should instead be deferred to when webpack runs, where it will resolve to the not-node code (crypto.js).
• So an explicit --external=@cosmjs/crypto was needed.