CI: one test binary per crate, line tables only, one WASM check (#2710)

* CI: dev profile keeps line tables for workspace crates and no debug info for dependencies

* Control server tests: persistent_requests_and_slow_replies_outlive_the_idle_read_timeout no longer races the idle timeout

Each request (and the closing half-shutdown) reaches the socket before the
worker reads, so on a slow machine only the reply waits outlast the 100 ms
idle timeout, as the test intends. The idle test sends its input the same
way, and the no-frames test allows 5 s instead of 2 s to give up.

* CI: one integration-test binary per crate

Each crate's tests/*.rs become modules of tests/it/main.rs (51 test files
into 13 binaries, plus 6 that stay their own). Inner #![cfg] attributes
move to the mod lines. Files that change state for the whole process keep
a binary of their own: codecs jxl_tail_heap and raw sr2_heap (dhat global
allocator), gpu shutdown, shutdown_first and memory, ui-egui shutdown.
Docs, comments and the GPU probe name the new paths and targets
(--test it <module>::); the CI report names an it binary's skips after
the crate.

* CI: tests under nextest, doctests apart, one wasm check

xtask ci runs the tests with cargo nextest run --lib --bins --tests when
cargo-nextest is installed, else cargo test with the same targets and a
one-line notice; doctests run after them with cargo test --workspace --doc.
The heif and hardware GPU steps use the same runner. Examples stay out of
the test build (clippy --all-targets still checks them). Concurrent tests
under nextest follow the RUST_TEST_THREADS cap (NEXTEST_TEST_THREADS).
The wasm check is one cargo check --keep-going over the same crates, and
clippy runs with --keep-going.

* CI: tests run under cargo test by default, nextest with LIGHTCRAFT_NEXTEST=1 (per-process scene cache)

README.zh-hans.md

@@ -357,7 +357,7 @@ CI 默认使用行表调试信息，并按启动时可用内存每 1.5 GB 开一
 （每个 CPU 最多一个；读不到内存时为 4 个），所以一台 8 GB、空闲 6 GB 的机器会用 4 个任务构建，
 而一台空闲内存很少的繁忙机器会用更少。测试线程数随之调整，上限为 4。否则，每个 CPU 一个的
 完整调试信息链接器会在任何测试运行之前就耗尽内存。GPU 覆盖范围不变。显式设置
-`CARGO_PROFILE_DEV_DEBUG`、`CARGO_BUILD_JOBS` 和 `RUST_TEST_THREADS` 会覆盖这些默认值。
+`CARGO_PROFILE_DEV_DEBUG`、`CARGO_BUILD_JOBS`、`RUST_TEST_THREADS` 和 `NEXTEST_TEST_THREADS` 会覆盖这些默认值。
 日常开发命令保持它们各自的设置。
 
 **内存受限机器上的 release 构建：** [#1196](https://github.com/storytold/lightcraft/issues/1196)