refactor(build): replace eslint/prettier with oxlint/oxfmt, add debug…

[imaTik0]

… build variant, remove checksum cache

Linting/formatting:

• Replace eslint + prettier with oxlint and oxfmt
• Add .oxlintrc.json and .oxfmtrc.json config files
• Remove eslint.config.mjs, prettier.config.js
• Update package.json: lint/format scripts; remove eslint/prettier devDeps; add oxlint

Debug/release build variants:

• Add PRIVMX_BUILD_TYPE CMake cache variable to all five C++ components (async-engine, webendpoint-cpp, drv-crypto, drv-ecc, drv-net)
• Debug: -O0 -g, ASSERTIONS=2, SAFE_HEAP=1, STACK_OVERFLOW_CHECK=2, no LTO
• Release: unchanged (-O3, LTO, ASSERTIONS=0, SAFE_HEAP=0)
• Add build:debug and build:wasm:debug npm scripts
• pipeline.sh reads PRIVMX_BUILD_TYPE from env; passes it to build_api
• build_api, build_async_engine, build_webdrivers read build type; reconfigure only when CMakeCache.txt is absent or the build type changed
• Add configure_if_needed helper in build_webdrivers to avoid repetition

Remove custom checksum cache:

• Delete scripts/check_dir_checksum
• Remove check_dir_checksum calls, RESULT case/esac blocks, and need_rebuild sentinel logic from build_gmp, build_poco, build_privmx_endpoint, build_pson, build_secp, build_api, build_async_engine, build_webdrivers
• Replace with: configure step guarded by CMakeCache.txt / Makefile existence; make always runs (Make's own dependency graph skips unchanged units)

Add clean:wasm script:

• scripts/clean_wasm removes build-emscripten/ from every first-party C++ component and all dependency_sources/ subdirectories
• Add "clean:wasm" npm script

README:

• Update build scripts table to include build:debug, build:wasm:debug, clean:wasm
• Add "Release vs Debug builds" section with flag comparison table