fix: proper use of add_unsafe in unconstrained

[guipublic]

Description

Problem*

Small fix which makes sure to use embedded_curve_add_unsafe() properly in underconstrained mode.

Summary*

Checking for infinity, it is easy to do in underconstrained function.

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

Changes to number of Brillig opcodes executed

Generated at commit: d7493d4a65534bd071098d3644751a4c3f75db32, compared to commit: fa28667e51e9891f34f7f67aa1ab814001845e3f

🧾 Summary (10% most significant diffs)

Program	Brillig opcodes (+/-)	%
multi_scalar_mul_inliner_min	+30,726 ❌	+66.16%
multi_scalar_mul_inliner_max	+10,529 ❌	+36.59%
multi_scalar_mul_inliner_zero	+10,529 ❌	+36.59%

---

Full diff report 👇

Program	Brillig opcodes (+/-)	%
multi_scalar_mul_inliner_min	77,167 (+30,726)	+66.16%
multi_scalar_mul_inliner_max	39,303 (+10,529)	+36.59%
multi_scalar_mul_inliner_zero	39,303 (+10,529)	+36.59%
inline_decompose_hint_brillig_call_inliner_min	188 (+35)	+22.88%
embedded_curve_ops_inliner_min	485 (+70)	+16.87%

[github-actions]

Changes to Brillig bytecode sizes

Generated at commit: d7493d4a65534bd071098d3644751a4c3f75db32, compared to commit: fa28667e51e9891f34f7f67aa1ab814001845e3f

🧾 Summary (10% most significant diffs)

Program	Brillig opcodes (+/-)	%
regression_5045_inliner_min	+39 ❌	+30.95%
inline_decompose_hint_brillig_call_inliner_min	+39 ❌	+28.06%

---

Full diff report 👇

Program	Brillig opcodes (+/-)	%
regression_5045_inliner_min	165 (+39)	+30.95%
inline_decompose_hint_brillig_call_inliner_min	178 (+39)	+28.06%
multi_scalar_mul_inliner_max	310 (+60)	+24.00%
multi_scalar_mul_inliner_zero	310 (+60)	+24.00%
multi_scalar_mul_inliner_min	337 (+39)	+13.09%
embedded_curve_ops_inliner_min	426 (+39)	+10.08%