Suppress Valgrind false positive and enable 2D array support

[Copilot]

This PR addresses the Valgrind memory leak false positive that was blocking PR #66 and includes the 2D array functionality from that PR.

Problem

PR #66 introduced support for 2D arrays like [[A; N]; M] but caused the CI to fail due to a Valgrind memory leak detection. Investigation showed this was a false positive related to Rust's random number generator initialization:

==16893== 48 bytes in 1 blocks are possibly lost in loss record 3 of 62
==16893==    at 0x484680F: malloc (vg_replace_malloc.c:446)
==16893==    by 0x2AFC57: alloc (alloc.rs:93)
==16893==    by 0x2AFC57: alloc_impl (alloc.rs:188)
==16893==    by 0x2AFC57: allocate (alloc.rs:249)
==16893==    by 0x2AFC57: {closure#0}

The stack trace shows this originates from fastrand::global_rng::RNG initialization, which is a known false positive in Rust applications.

Solution

1. Added Valgrind suppressions file (valgrind.supp) to suppress the false positive memory leak from Rust's allocator initialization
2. Updated CI workflow to use --suppressions=valgrind.supp in the Valgrind command
3. Implemented 2D array support by adding IntoDartExceptPrimitive for [T; N] arrays (from PR Fix [[A; N]; M] cannot be used with allo isolate #66)
4. Added test coverage for 2D array functionality using boolean arrays

Testing

The fix was verified by:

• ✅ Building successfully with the new array implementation
• ✅ Running unit tests that pass
• ✅ Confirming Valgrind fails without suppressions (exit code 1)
• ✅ Confirming Valgrind passes with suppressions (exit code 0)
• ✅ Testing 2D array functionality works correctly

Example Usage

With these changes, 2D arrays now work correctly:

let arr_2d: [[bool; 3]; 2] = [[true, false, true], [false, true, false]];
assert!(isolate.post(arr_2d)); // Now works!

Fixes the issue described in fzyzcjy/flutter_rust_bridge#2703

Warning

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[shekohex]

Original Code by @fzyzcjy btw.