cli: mirror Cargo's implicit strip default when manually stripping binaries (fixes wasm-opt SIGABRT)

[nicoburns]

Summary

Fixes #5119 (wasm-opt failed with status code signal: 6 (SIGABRT) / compile unit size was incorrect on dx build --web --release).

Root cause: since #4966 (0.7.2), dx always builds with --config profile.<x>.strip=false (to keep manganis symbols alive) and relies on post_process_executable/get_strip_setting to strip manually afterwards. But get_strip_setting only honored an explicit strip key in Cargo.toml and returned StripSetting::None otherwise — it didn't replicate Cargo's implicit default (since Rust 1.77, Cargo strips debuginfo when the profile's debuginfo is disabled, as release is by default). So ~1.3MB of DWARF from the precompiled std stayed in release wasm. wasm-bindgen (--keep-debug, on by default via --debug-symbols) then rewrites that DWARF, and binaryen's wasm-opt aborts trying to re-emit it (DWARFEmitter.cpp:201). In 0.7.1 the linker stripped the debuginfo (Cargo's default), which is why the same flags worked there.

Change in get_strip_setting, after resolving the profile's inherits chain:

explicit strip in profile chain  -> use it (as before)
otherwise                        -> resolve `debug` in profile chain
                                    (default: release=off, dev=full)
   debug off  -> StripSetting::Debuginfo   // Cargo's implicit default
   debug on   -> StripSetting::None

Verification

• Minimal repro (wasm-bindgen 0.2.126 + binaryen): strip=false build → wasm-bindgen --keep-debug → wasm-opt --debuginfo reproduces the exact SIGABRT; the same wasm without the wasm-bindgen rewrite, or with Cargo's default strip, passes.
• Unpatched dx from main reproduces the failure on a hello-world web app in --release; with this patch the build succeeds and the output wasm contains no .debug_* sections (1.6MB → 471KB).
• wasm-split builds are unaffected (post_process_executable still returns early), as are dev builds (debug resolves to full → no strip).

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/819f3522f488427cb8df5f6e12b5af56
Requested by: @nicoburns

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