perf(snapshot): minify snapshot sources

[nathanwhit]

Summary

This adds build-time minification for extension sources used by the startup snapshot.

When DENO_SNAPSHOT_MINIFY_SOURCES=1 is set, the snapshot build transpiles sources as before, then runs them through Rolldown's minifier with compression and name mangling disabled. This keeps the transform conservative: it removes whitespace/comments without changing binding names or applying semantic compression.

The minifier is applied to both sources consumed during snapshot creation and residual lazy extension sources emitted by cli/snapshot/build.rs. The minified output is asserted to be ASCII at snapshot build time.

Release CI now sets DENO_SNAPSHOT_MINIFY_SOURCES=1 for the release artifact builds and the benchmark release build, so release binaries exercise this path.

Why

Startup snapshot sources include a large amount of JavaScript/TypeScript text. Minifying those sources substantially reduces the serialized snapshot payload and residual embedded source size, even though it does not meaningfully reduce the deserialized V8 heap graph.

Measurements

Measured on a debug build from main@upstream with:

cargo build --bin deno -p deno
DENO_SNAPSHOT_MINIFY_SOURCES=1 cargo build --bin deno -p deno

Results:

CLI_SNAPSHOT.bin
7,149,430 -> 5,052,953
shrinks by 2,096,477 bytes = 29.32%

residual_sources
2,207,336 -> 1,387,948
shrinks by 819,388 bytes = 37.12%

combined file bytes
9,356,766 -> 6,440,901
shrinks by 2,915,865 bytes = 31.16%
2.78 MiB / 2.92 MB smaller

profile-deserialization bytes
2,710,184 -> 2,714,856
grows by 4,672 bytes = 0.17%

Validation

cargo build --bin deno -p deno
DENO_SNAPSHOT_MINIFY_SOURCES=1 cargo build --bin deno -p deno
deno check --lock=./tools/deno.lock.json .github/workflows/ci.ts

Also smoke-tested the minified debug binary with basic execution, node:path, URL, ReadableStream, and Deno.readTextFile.

[bartlomieju]

Is this even reachable? I thought we have a check that ensures everything is ascii