Fix TOB-25: validate ECDSA edge cases and add regression tests

[Stephen-Thomson]

Description of Changes

This PR completes the remediation for TOB-25 by validating ECDSA behavior around scalar multiplication and edge-case point handling.
Additional regression tests were added to ensure invalid or degenerate inputs cannot produce incorrect signatures or verification results.

The tests exercise:

• Scalar multiplication edge cases
• Correct handling of infinity points
• Validation behavior during signature verification

Linked Issues / Tickets

• Addresses TOB-25 (internal security ticket)

Testing Procedure

• Added targeted ECDSA unit tests covering TOB-25
• All tests pass locally
• Verified behavior manually during development

• I have added new unit tests
• All tests pass locally
• I have tested manually in my local environment

Checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have updated CHANGELOG.md with my changes
• I have run npm run doc and npm run lint one final time before requesting a review
• I have fixed all linter errors to ensure these changes are compliant with ts-standard
• I have run npm version patch so that my changes will trigger a new version to be released when they are merged

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[github-actions]

🏁 Benchmark Comparison (Node 22)

Comparing this PR (08d569f) against master (1e0cc5c).

✅ No regressions over the 5% threshold detected.

Benchmark	Metric	PR Branch	Master	Δ	Change
BigNumber Arithmetic	mul large numbers	8.83 ms	8.81 ms	+0.02 ms	+0.23%
BigNumber Arithmetic	add large numbers	1.45 ms	1.45 ms	+0.00 ms	0.00%
BigNumber Serialization	toSm big	2.94 ms	2.83 ms	+0.11 ms	+3.89%
BigNumber Serialization	toSm little	3.01 ms	2.92 ms	+0.09 ms	+3.08%
BigNumber Serialization	fromSm big	3.07 ms	2.98 ms	+0.09 ms	+3.02%
BigNumber Serialization	fromSm little	3.14 ms	3.03 ms	+0.11 ms	+3.63%
BigNumber Serialization	fromScriptNum	3.17 ms	3.05 ms	+0.12 ms	+3.93%
Script Serialization	Big script round trip	3.85 ms	3.77 ms	+0.08 ms	+2.12%
Transaction Verification	deep chain verify	443.31 ms	441.72 ms	+1.59 ms	+0.36%
Transaction Verification	wide transaction verify	458.80 ms	454.87 ms	+3.93 ms	+0.86%
Transaction Verification	large tx verify	228.04 ms	225.39 ms	+2.65 ms	+1.18%
Transaction Verification	nested inputs verify	104.46 ms	103.62 ms	+0.84 ms	+0.81%
Symmetric Key	encrypt large 2MB	1526.09 ms	1558.81 ms	-32.72 ms	-2.10%
Symmetric Key	decrypt large 2MB	1518.63 ms	1564.10 ms	-45.47 ms	-2.91%
Symmetric Key	encrypt 50 small	6.55 ms	6.87 ms	-0.32 ms	-4.66%
Symmetric Key	decrypt 50 small	6.38 ms	6.59 ms	-0.21 ms	-3.19%
Symmetric Key	encrypt 200 medium	157.27 ms	161.17 ms	-3.90 ms	-2.42%
Symmetric Key	decrypt 200 medium	156.84 ms	160.19 ms	-3.35 ms	-2.09%
Reader & Writer	mixed ops	0.22 ms	0.23 ms	-0.01 ms	-4.35%
Reader & Writer	large payloads	28.09 ms	28.51 ms	-0.42 ms	-1.47%
Reader & Writer	3000 small payloads	1.73 ms	1.73 ms	+0.00 ms	0.00%
Reader & Writer	400 medium payloads	15.00 ms	14.91 ms	+0.09 ms	+0.60%
Atomic BEEF	Transaction.toAtomicBEEF	1.48 ms	1.49 ms	-0.01 ms	-0.67%
Atomic BEEF	Transaction.fromAtomicBEEF	3.56 ms	3.64 ms	-0.08 ms	-2.20%