fix(vpto): add SIMT fastmath control

[Zhendong404]

Summary

• Add --simt-fastmath, disabled by default.
• Pass --cce-simt-fpmath-combine=false to Bisheng by default and enable it only when explicitly requested.
• Add CLI regression coverage for the new option.

Validation

• PTOAS compiler shared library builds successfully.
• ptoas --simt-fastmath --help and ptoas --simt-fastmath=false --help succeed.
• The issue-1117 mul/add repro emits different objects for default and --simt-fastmath modes.
• Default LLVM IR remains separate fmul and fadd operations.

Scope

This PR addresses the implicit SIMT mulf + addf contraction described in issue #1117. The scalar high-precision fdiv question remains open: CANN 9.0.0 exposes high-precision division only through vector bisheng::cce::simd::hp::vdiv / PTO Div754-style helpers; the candidate scalar LLVM intrinsics are not selectable on the current A5 Bisheng target.

Refs #1117

[reedhecre]

A5 板测失败

• 触发方式：merged
• 源码提交：53da58f4b57b
• 结果汇总：OK 20 / FAIL 1 / SKIP 0
• 日志：/root/ptoas-board-monitor-a5/logs/20260812_110505_merged_pr1138.log
• 结果 TSV：/root/ptoas-board-monitor-a5/logs/20260812_110505_merged_pr1138.tsv
• 失败阶段：board-validation-qwen / exit=1

失败用例

• rope_kv_cache (run, exit=2)

[reedhecre]

A3 板测失败

• 触发方式：merged
• 源码提交：53da58f4b57b
• 结果汇总：OK 218 / FAIL 2 / SKIP 3
• 日志：/home/zhongxuan/ptoas-board-monitor/runtime/logs/20260811_200435_merged_pr1138.log
• 结果 TSV：/home/zhongxuan/ptoas-board-monitor/runtime/logs/20260811_200435_merged_pr1138.tsv
• 失败阶段：board-validation / exit=1

失败用例

• ci (run, exit=2)
• gather_legacy (run, exit=1)

[reedhecre]

A3 板测失败详情：PR #1138

ci

stage=run info=exit=2

[ERROR] Mismatch: golden_v1.bin vs v1.bin, max diff=2.0 at idx=0 (golden=1, out=-1, dtype=int32)
[ERROR] compare failed
[2026-08-11 20:29:48] ERROR: testcase failed (exit 2): ci

gather_legacy

stage=run info=exit=1

[ERROR] aclrtSynchronizeStream(stream) failed: 507035 (/home/zhongxuan/ptoas-board-monitor/runtime/runs/20260811_200435_merged_pr1138/npu_validation/Gather/gather_legacy/main.cpp:114)
[ERROR] RecentErrMsg: EZ9999: Inner Error!
EZ9999[PID: 4069118] 2026-08-11-20:33:45.020.644 (EZ9999):  The error from device(chipId:2, dieId:1), serial number is 252, there is an exception of aivec error, core id is 47, error code = 0x4000000000000000, dump info: pc start: 0x124a00000000, current: 0x124a00000094, vec error info: 0xf01d, mte error info: 0x350300402d, ifu error info: 0x212d052480440, ccu error info: 0x3800059, cube error info: 0, biu error info: 0, aic error mask: 0x6500020bd00028c, para base: 0x12c100000000.[FUNC:PrintCoreInfo][FILE:device_error_core_proc.cc][LINE:645]
        TraceBack (most recent call last):
       The extend info: errcode:(0x4000000000000000, 0, 0) errorStr: VEC instruction error: the ub address out of bounds. fixp_error0 info: 0x300402d, fixp_error1 info: 0x35, fsmId:1, tslot:0, thread:0, ctxid:0, blk:0, sublk:0, subErrType:4.[FUNC:PrintCoreInfo][FILE:device_error_core_proc.cc][LINE:658]
       Kernel task happen error, retCode=0x31, [vector core exception].[FUNC:PreCheckTaskErr][FILE:davinci_kernel_task.cc][LINE:1729]
       AIV Kernel happen error, retCode=0x31.[FUNC:GetError][FILE:stream.cc][LINE:1475]
       [AIC_INFO] after execute:args print end[FUNC:GetError][FILE:stream.cc][LINE:1475]
       [DFX_INFO]Aicore kernel execute failed, device_id=5, stream_id=46, report_stream_id=46, task_id=0, flip_num=0, fault kernel_name=vec_add_scalar_kernel_2d, fault kernel info ext=vec_add_scalar_kernel_2d, program id=0, hash=13985294925899954301.[FUNC:GetError][FILE:stream.cc][LINE:1475]
       rtStreamSynchronize execution failed, reason=vector core exception[FUNC:FuncErrorReason][FILE:error_message_manage.cc][LINE:65]
       synchronize stream failed, runtime result = 507035[FUNC:ReportCallError][FILE:log_inner.cpp][LINE:148]
[2026-08-11 20:33:47] ERROR: testcase failed (exit 1): gather_legacy