fix: replace moonbitlang/core/strconv with core/string

[bobzhang]

moonbitlang/core 0.10.12 removed moonbitlang/core/strconv — only core/internal/strconv remains. Any module depending on mocket now fails package solving before a single file is compiled:

Error: Failed to calculate build plan
Caused by:
    0: Failed to solve package relationship
    1: Cannot find import 'moonbitlang/core/strconv' in oboard/mocket@0.9.1

I hit this from downstream — an example in rabbita that depends on mocket stopped resolving on the nightly toolchain.

core/string carries the same API on both 0.10.11 and 0.10.12, so this builds on current stable and nightly.

Changes

• moon.pkg (root) imported core/strconv, but nothing in the package references @strconv — the import was dead. The package already imports core/string, so this is just a deletion.
• benchmarks/mocket, benchmarks/mocket_middleware, examples/route each parse a port. They switch to @string.from_str, which is the same FromStr trait method exposed as a free function (#as_free_fn), so the call sites keep their inferred-type form:

-      let port : Int = @strconv.from_str(port_text) catch { _ => 3000 }
+      let port : Int = @string.from_str(port_text) catch { _ => 3000 }

7 files, +6/−7.

Verification

toolchain	state	moon check --target native
nightly v0.10.11+9de356786-nightly	main	exit 255 — Cannot find import 'moonbitlang/core/strconv'
nightly v0.10.11+9de356786-nightly	this branch	exit 0
stable v0.10.11+6ff76a5f9	this branch	exit 0 (js and native)

moon test --target js,native on this branch: 105 passed (js), 100 passed (native).

Heads-up, unrelated to this PR

While running your CI steps locally on the current stable toolchain (moon 0.1.20260827 / moonc v0.10.11+6ff76a5f9), two of them fail on main itself, with this branch stashed:

1. moon check --deny-warn — exit 255:

   internal/header/header.mbt:41:13
     let buf = StringBuilder::new()
     Warning (deprecated): Use `StringBuilder()` instead
   

2. moon fmt + git diff --exit-code — the formatter rewrites a number of files (content_type.mbt, cookie.mbt, dispatch.mbt, middleware.mbt, mocket.js.mbt, …).

Your last green run was 2026-08-22, so I think the toolchain has moved since. I deliberately left both alone to keep this PR reviewable rather than burying a 7-line fix under unrelated reformatting — happy to send either as a separate PR if useful.

🤖 Generated with Claude Code

https://claude.ai/code/session_01AmoyPMELemz5hdNNdXyAkm

[bobzhang]

CI on this PR is red, but not because of anything it changes — it fails at step 6 of 10:

internal/header/header.mbt:41:13
  let buf = StringBuilder::new()
  Error Warning (deprecated): Use `StringBuilder()` instead

internal/header/header.mbt isn't touched here. And because moon check fails, steps 7–10 are skipped, so moon test never ran — this PR has no test signal at all through CI.

I confirmed it is pre-existing by stashing this branch and running the same gate against main alone: it fails identically.

I've opened #33 with the two fixes that restore green CI (the StringBuilder deprecation, and a moon fmt pass), kept separate so this stays a 7-line change. With #33 as the base, this PR's change passes all four gates locally — --deny-warn exit 0, fmt --check exit 0, 105 tests (js) and 100 (native).

So this should go green on a rebase once #33 lands, with no changes needed here. Ordering is the only dependency.

🤖 Generated with Claude Code

https://claude.ai/code/session_01AmoyPMELemz5hdNNdXyAkm