[ChrisJr404]

Closes #2683.

Problem

YAML scalars tagged !!float were round-tripped through float64 and re-serialized by Go's JSON encoder, which strips the decimal part of whole-number floats. The reporter's example:

percentiles: [50.0, 95.0, 99.0, 99.9]

was emitted as:

{"percentiles":[50,95,99,99.9]}

JSON does not distinguish ints from floats at the syntactic level, but every common library (Go's encoding/json, Python's json, jq) preserves the fractional form of values that came in as floats. yq's YAML decoder already parses these scalars as !!float with the original text intact, so the encoder can emit them verbatim instead of round-tripping through a float64.

Fix

MarshalJSON on ScalarNode now special-cases !!float:

• If the scalar's Value is already a JSON-shaped number literal containing a . or exponent (e.g. 50.0, 99.9, 1.5e-3, -7.0), it is emitted verbatim.
• If Value is an integer-shaped string tagged !!float (e.g. !!float 5), it is formatted with strconv.FormatFloat and .0 is appended so the output is still a JSON number with a fractional part (5.0).
• Otherwise (empty Value, parse error, or non-finite result) the code falls back to the existing path, so the current behaviour for .inf / .nan is unchanged and stays a separate issue.

!!int nodes go through the unchanged path and still encode as JSON integers.

Behaviour after the fix

$ echo 'percentiles: [50.0, 95.0, 99.0, 99.9]' | ./yq -o json -I 0 '.'
{"percentiles":[50.0,95.0,99.0,99.9]}

$ echo 'a: 50' | ./yq -o json -I 0 '.'
{"a":50}

$ echo 'a: !!float 5' | ./yq -o json -I 0 '.'
{"a":5.0}

$ echo 'a: 1.5e-3' | ./yq -o json -I 0 '.'
{"a":1.5e-3}

$ echo 'a: [1, 2.0, 3, 4.5]' | ./yq -o json -I 0 '.'
{"a":[1,2.0,3,4.5]}

Scope notes

• This only changes YAML to JSON. The JSON to YAML direction still collapses 50.0 to 50 in the JSON decoder (setScalarFromJson in pkg/yqlib/candidate_node_json.go), and the existing "numbers" decode test in json_test.go codifies that. Changing that direction would be a larger, opinionated change and is out of scope here.
• Special floats (.inf, .nan) are left on the existing error path; the YAML to JSON conversion for those values was already broken (strconv.ParseFloat: parsing ".inf": invalid syntax) and is a separate problem.

Tests

Added six scenarios to jsonScenarios in pkg/yqlib/json_test.go:

• preserve whole-number floats including the reporter's [50.0, 95.0, 99.0, 99.9] case (documented scenario)
• !!int whole numbers stay integers
• !!float 5 becomes 5.0
• scientific notation preserved
• negative floats preserved
• mixed int and float arrays encode each value with the right shape

go test ./... is green locally.