fix: don't silently use 0 when a wire price/size fails to parse (market order at 0)

[chiliec]

Description

parseFloat returns 0.0 on any parse error (it swallows the error). Two call sites use it for financial values coming off the API, where a silent 0 is dangerous:

1. SlippagePrice — market order price. For a market order (px == nil) it parses the mid price:

price = parseFloat(midPriceStr)

A malformed mid price from AllMids becomes 0, and the caller places a market order priced at 0 with no error surfaced.

2. MarketClose — position size. It parses the position size:

szi := parseFloat(pos.Szi)

A malformed pos.Szi becomes 0, so size = abs(0) = 0 — a no-op / wrong close, again silently.

Fix

Add parseFloatStrict (error-returning) and use it at both sites. Both SlippagePrice and MarketClose already return an error, so the parse failure now propagates instead of turning into a 0. parseFloat is left unchanged for its existing display callers, so this is non-breaking.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Testing

• Added TestParseFloatStrict — valid inputs match parseFloat; invalid inputs error instead of silently returning 0
• go test ./ passes (full suite)
• go vet ./ and gofmt clean

Code Quality

• Follows project style
• Self-reviewed
• Commented the strict helper and why it exists
• No new warnings

Additional Notes

First-time contributor. parseFloat's third caller is a display/formatting path where a 0 default is harmless, so I left it as-is — happy to convert that too if you'd prefer all parses to be strict.