fix(iSTA): preserve output uncertainty and conditional SDF period checks

[yipeix]

Output timing checks ignored the uncertainty of the clock associated with set_output_delay, making setup and hold slack optimistic. Apply setup uncertainty with a negative sign and hold uncertainty with a positive sign when calculating required time, and make the report increments add up for nonzero and negative output delays.

SRAM minimum-period checks also lost their Liberty sdf_cond during SDF export. Preserve the condition around the PERIOD pin event so distinct read/write requirements on the same clock pin do not become conflicting unconditional checks. Existing check values and unconditional formatting are preserved.

The branch includes main commit f8036144b through merge commit da42c5393. The production diff is limited to TimingAnalyzer.cpp, TimingReporter.cpp and SDFWriter.cpp.

Validation:

• ecc_bin builds and five focused CTests pass. The new conditional PERIOD regression fails on the previous writer and passes after the fix; it covers distinct read/write limits and an unconditional check.
• GCD TT/SS SDF files are identical to the previous fixed baseline except for the generation date.
• example6 TT/SS SDF files change only eight conditional SRAM PERIOD entries per corner; all numeric values and detailed timing reports are unchanged.
• SDF export/comparison tooling is available in the local example directories. Actual PrimeTime SDF numerical comparison is pending export on the licensed server; these rerun checks do not claim agreement with PrimeTime.
• As requested, test-directory changes remain local and are excluded from this PR.