feat!: add support for file fields in forms

[m4tx]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 92.53438% with 38 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cot/src/form/field_value.rs	83.14%	15 Missing ⚠️
cot/src/form.rs	92.98%	4 Missing and 8 partials ⚠️
cot/src/form/fields/files.rs	93.15%	8 Missing and 2 partials ⚠️
cot/src/form/fields.rs	98.93%	0 Missing and 1 partial ⚠️

Flag	Coverage Δ
rust	88.14% <92.53%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cot-macros/src/admin.rs	89.58% <ø> (ø)
cot-macros/src/form.rs	96.72% <100.00%> (ø)
cot/src/admin.rs	73.42% <100.00%> (-0.25%)	⬇️
cot/src/error.rs	88.05% <ø> (ø)
cot/src/html.rs	97.59% <100.00%> (+0.02%)	⬆️
cot/src/openapi.rs	93.47% <100.00%> (-0.18%)	⬇️
cot/src/request.rs	95.91% <ø> (-0.17%)	⬇️
cot/src/form/fields.rs	87.36% <98.93%> (+0.69%)	⬆️
cot/src/form/fields/files.rs	93.15% <93.15%> (ø)
cot/src/form.rs	92.94% <92.98%> (+5.44%)	⬆️
... and 1 more

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[seqre]

LGTM in general, I'd like to get answers first before approving though