Improve RzIL floating-point support

[b1llow]

Your checklist for this pull request

• I've read the guidelines for contributing (https://github.com/rizinorg/rizin/blob/dev/CONTRIBUTING.md) to this repository.
• I made sure to follow the project's coding style (https://github.com/rizinorg/rizin/blob/dev/DEVELOPERS.md#code-style).
• I've documented every RZ_API function and struct this PR changes.
• I've added tests that prove my changes are effective (required for changes to RZ_API).
• I've updated the Rizin book (https://github.com/rizinorg/book) with the relevant information (if needed).
• I've used AI tools to generate fully or partially these code changes and I'm sure the changes are not copyrighted by somebody else.

Detailed description

This PR improves IEEE-754 edge-case handling in RzFloat and adds reusable floating-point facilities to RzIL.

The RzFloat changes fix:

• binary80 explicit-integer-bit and NaN handling;
• binary16 conversions;
• gradual underflow and directed rounding;
• overflow and inexact exception reporting;
• propagation of floating-point exception metadata through nested conversions.

The RzIL changes add scoped binary80 precision support through RzFloatRPrecision and the FWITH_RPREC opcode. Precision scopes restore the previous SoftFloat state after
successful evaluation and after evaluation failures. The new opcode is supported by validation, duplication, destruction, string and JSON exporters, graph output, and VM
evaluation.

This PR also adds runtime rounding-mode constructors for conversion, rounding, square root, addition, subtraction, multiplication, division, and remainder operations. The
rounding mode is represented by a 32-bit IL bitvector whose values correspond to RzFloatRMode. RNE, RNA, RTP, RTN, and RTZ are supported; unknown values fall back to RNE. These
helpers expand to ordinary LET/ITE expressions and do not introduce a dynamic rounding-mode opcode.

Finally, FEXCEPT now emits a VM event only when the queried exception is actually present, while preserving exceptions raised by nested conversions.

No Rizin book update is needed because this PR does not change user-facing commands or workflows.

Test plan

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Closing issues

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[codecov]

Codecov Report

❌ Patch coverage is 44.39776% with 397 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.01%. Comparing base (12cf18e) to head (7cc8df1).

Files with missing lines	Patch %	Lines
librz/util/float/float.c	57.14%	61 Missing and 11 partials ⚠️
librz/il/il_export_string.c	19.75%	63 Missing and 2 partials ⚠️
librz/il/il_validate.c	27.38%	52 Missing and 9 partials ⚠️
librz/il/il_graph.c	8.77%	52 Missing ⚠️
librz/il/il_opcodes.c	41.55%	26 Missing and 19 partials ⚠️
librz/il/il_export_json.c	27.11%	43 Missing ⚠️
librz/il/il_export_string_unicode.c	5.12%	36 Missing and 1 partial ⚠️
librz/il/theory_fbasic.c	89.23%	8 Missing and 6 partials ⚠️
librz/il/definitions/float.c	30.00%	6 Missing and 1 partial ⚠️
librz/util/float/float_internal.c	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
librz/il/il_vm_eval.c	60.00% <ø> (+1.42%)	⬆️
librz/include/rz_util/rz_float.h	50.00% <ø> (ø)
librz/util/float/float_internal.c	67.74% <88.88%> (+1.75%)	⬆️
librz/il/definitions/float.c	62.50% <30.00%> (-5.25%)	⬇️
librz/il/theory_fbasic.c	69.16% <89.23%> (+14.14%)	⬆️
librz/il/il_export_string_unicode.c	49.07% <5.12%> (-3.84%)	⬇️
librz/il/il_export_json.c	37.73% <27.11%> (+1.08%)	⬆️
librz/il/il_opcodes.c	56.56% <41.55%> (-1.37%)	⬇️
librz/il/il_graph.c	27.36% <8.77%> (+0.63%)	⬆️
librz/il/il_validate.c	58.02% <27.38%> (-5.01%)	⬇️
... and 2 more

... and 11 files with indirect coverage changes

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