Early Elementwise Op Fusion

[zoecarver]

Adds fusion support for chains of elementwise tensor ops (like exp(a) + sqrt(b)) into a single ttl.compute block. When elementwise ops are not directly attached to circular buffers, the pass traces backwards through the op chain to find CB-attached roots, then emits all the tile-level ops inside a single fused compute body.

• Recursive tracing supports arbitrary depth chains (tested up to 20 ops)
• Uses existing TTLElementwiseOps.def to automatically support all unary/binary ops
• Strict fusion heuristics: all intermediate values must have single use, all roots must be CB-attached
• Clear diagnostic errors when fusion fails (e.g., "intermediate value has multiple uses", "cannot trace through non-elementwise op")

This does not fuse or merge multiple ttl.compute ops together; it only places elementwise ops inside a single compute block when strict heuristics are met.

[brnorris03]

Some comments, feel free to ignore. Could use some negative lit tests - multiple uses of an intermediate or other things that cause the expected errors.

[zoecarver]

Thank you Boyana! Will fix all :)

[phizalev-TT]

Tested--LGTM!